--- slug: the-water-between-you-and-the-sewer passed: 2026-11-01 by: ccr-81332fb3-8nrbtu wave, one independent agent on oversight/claims-pass.md (pre-deploy; reader check on local copies with AW_DIR; every source-record entry read against its kept copy and live source) checked: 146 confirmed: 127 wrong: 1 unverifiable: 0 observed: 18 stale: 0 --- # Claims pass: The Water Between You and the Sewer Live page: not deployed yet; step 2 skipped. Reader check (pre-deploy, local copies): `AW_DIR= node verify-the-water-between-you-and-the-sewer.mjs`, run with the verifier copied into a second empty directory: exit 0, 290 passed, 0 failed (inside the repository, with the kept-copy and frontmatter checks: exit 0, 370 passed, 0 failed; `--mutate` from the empty directory: exit 1, 464 passed, 8 failed, as it must). The page prints no transcript of the verifier. Step 6, sentence-only edits in scratch copies, one at a time, plain run: every one caught (exit 1): the visible dek's 52% to 53% (the head copies then disagree and the sentence fails), 46.1% to 46.4%, (490 Pa) to (491 Pa), fifteen to sixteen times, 52.4% to 52.9%, 1.630 to 1.639, 41% to 47%, 10.16 to 10.18 mm, 0.39 to 0.38 inch, 3 to 4 inches of back pressure, nine to eight people, three to four families, eight to nine soil stacks (quotation check). The verifier also passed with copies of the aw-* blocks, the record.js tag, the Cloudflare beacon and the pulse script injected into a scratch copy (exit 0, 290 passed), and failed when a figure was then planted (41% to 44%: exit 1). Mutation sweep: the-water-between-you-and-the-sewer: 240 mutated, 240 caught, 0 survived (text 0, meta 0, year 0). `assay/sources.mjs the-water-between-you-and-the-sewer --online`: 106 UNREADABLE, 15 FOUND, 14 in the repository (offline: sound; `scripts/check-sources.mjs`: 135 claims, 0 with no source found). Every UNREADABLE is a PDF. All eight PDFs were downloaded again on 2026-11-01 (each byte-identical, by sha256, to the copy the builder worked from) and text-extracted; every excerpt was found in its kept copy; the born-digital Hong Kong reports, Approved Document H and the PubMed abstracts matched the page's quotations character for character in the live text. For the four scanned works (BMS126, Monograph 31, BH13, and Cosgrove through archive.org's page images) every quoted or excerpted passage was read on page images rendered at 110 to 300 dpi; where the OCR disagrees ("ail", "onehalf", an extra comma after "system", interleaved columns, garbled fractions) the image agrees with the page. All four rows of p. 10 were read cell by cell against nbs1951.json and the verifier's typed fractions. After the fixes below (fixer, round 2, 2026-11-01): in the repository exit 0, 373 passed, 0 failed; from an empty directory with AW_DIR holding only the four files, exit 0, 293 passed, 0 failed; `--mutate` exit 1, 8 checks failed on the mutant. Scratch-copy sentence edits each fail (exit 1): "six wrong figures" to five, "one in a copy of nbs1951.json" to two, the visible dek's "come to 45%" to 46%, and "45% to 52%" to "45% to 53%" in all five page copies. With the aw-* blocks, record.js, the beacon and the pulse script injected: exit 0, 375 passed; with 45% then planted as 44%: exit 1. Mutation sweep: 241 mutated, 241 caught, 0 survived (text 0, meta 0, year 0). make_kept.py, rerun in a scratch directory on the same downloads, remakes all 18 kept files byte-identically. After the fixes below (fixer, round 3, 2026-11-01): in the repository exit 0, 373 passed, 0 failed; from an empty directory with AW_DIR holding only the four files, exit 0, 293 passed, 0 failed; `--mutate` exit 1, 8 checks failed on the mutant. Each of the six page plants applied alone to a scratch copy: exit 1. With the aw-* blocks, record.js, the beacon and the pulse script injected: exit 0, 375 passed; with 46.1% then planted as 46.4%: exit 1. `scripts/check-sources.mjs`: 136 claims, 0 with no source found. Mutation sweep: 241 mutated, 241 caught, 0 survived (text 0, meta 0, year 0). Playwright at 390, 768 and 1440 px: no console errors, no horizontal overflow, no third-party request. ## Claims - CONFIRMED | In 1951 the US National Bureau of Standards put the purpose of that water in two sentences | https://nvlpubs.nist.gov/nistpubs/Legacy/BMS/nbsbuildingmaterialsstructures126.pdf (title page image, PDF p. 3) | title page: "Issued October 15, 1951"; the two sentences are the Foreword (PDF p. 5), signed by the NBS Director - CONFIRMED | This water seal is normally from 2 to 4 inches in depth and is sufficient to prevent the passage of sewer air into the building under any ordinary conditions. | https://nvlpubs.nist.gov/nistpubs/Legacy/BMS/nbsbuildingmaterialsstructures126.pdf (Foreword image, PDF p. 5, p. III) | read on the page image, character for character: "The purpose of the trap is to interpose ... under any ordinary conditions." (pdftotext interleaves the lines; the image is the authority) - CONFIRMED | Foreword, signed E. U. Condon, Director, to J. L. French and H. N. Eaton, Self-Siphonage of Fixture Traps (NBS BMS126, 1951), p. III | https://nvlpubs.nist.gov/nistpubs/Legacy/BMS/nbsbuildingmaterialsstructures126.pdf (PDF p. 5) | signature "E. U. CONDON, Director." under the Foreword, p. III; title page "John L. French and Herbert N. Eaton", "Building Materials and Structures Report 126", 1951 - CONFIRMED | England's building guidance, Approved Document H (2015 edition), lists a 75 mm seal for a washbasin or sink and 50 mm for a bath, shower or WC pan | https://assets.publishing.service.gov.uk/media/5a80cf9ded915d74e33fc8ae/BR_PDF_AD_H_2015.pdf (p. 6, Table 1) | Table 1 "Minimum trap sizes and seal depths": Washbasin/Bidet 75; Bath/Shower 50; Sink 75; WC pan (both outlets) 50 (mm). Table gives minimum depths, with footnoted reductions (50 mm basins with flush grated wastes; 38 mm to a gully); the page does not say otherwise - CONFIRMED | 50 mm (England: bath, shower, WC) | https://assets.publishing.service.gov.uk/media/5a80cf9ded915d74e33fc8ae/BR_PDF_AD_H_2015.pdf (p. 6, Table 1) | "Bath 2 Shower 2 40 50"; WC pan rows "50"; Washbasin and Sink rows "75" - CONFIRMED | 2 in. (US recommended code of 1928: least) | https://nvlpubs.nist.gov/nistpubs/Legacy/BH/nbsbuildinghousing13.pdf (page image, PDF p. 44, printed p. 26) | Sec. 59, Water Seal: "Each fixture trap shall have a water seal of not less than 2 inches and not more than 4 inches." (Article V of the recommended code, report revised August 30, 1928) - CONFIRMED | with the water down to the dip in both legs, French and Eaton wrote | https://nvlpubs.nist.gov/nistpubs/Legacy/BMS/nbsbuildingmaterialsstructures126.pdf (page image, PDF p. 13, p. 7) | "When it has reached the value unity, this means that the water has been removed from both legs of the trap down to the dip of the trap and that minute changes of pressure in the proper direction will suffice to force sewer gas into the building." Quotation exact - CONFIRMED | A later Bureau monograph defines the depth in words it took from the American Standard National Plumbing Code of 1955 | https://nvlpubs.nist.gov/nistpubs/Legacy/MONO/nbsmonograph31.pdf (page image, PDF p. 6, p. 2) | "The trap seal is the maximum vertical depth of liquid that a trap will retain, measured between the crown weir and the top of the dip of the trap." exact; no asterisk on this definition (zoomed image) - CONFIRMED | in words it took from the American Standard National Plumbing Code of 1955 | https://nvlpubs.nist.gov/nistpubs/Legacy/MONO/nbsmonograph31.pdf (page image, PDF p. 6, p. 2) | "Except for those that are marked with an asterisk, the definitions have been taken from the American Standard National Plumbing Code A40.8-1955 [1]." - CONFIRMED | by the conventional definition, 1 mm of water is 9.80665 pascals | https://www.nist.gov/pml/special-publication-811/nist-guide-si-appendix-b-conversion-factors/nist-guide-si-appendix-b8 | live table row: "millimeter of water, conventional (mm H 2 O) 12 pascal (Pa) 9.806 65 E+00" - OBSERVED | For a 50 mm seal that is a pull of 50 mm of water (490 Pa) and a push of 100 mm (981 Pa) | recreated: node -e "console.log(50*9.80665, 100*9.80665)" | 490.33 and 980.665, shown as 490 Pa and 981 Pa; verifier section C and the 240-site sweep catch a change to either - OBSERVED | so a pull of s leaves a seal of t − s/2 | recreated: engine afterSuction(50,50,40) = 30 and the verifier's independent stepped model (section A, 290/290 pass from an empty directory) | a pull s < t leaves t - s/2; s >= t leaves t/2; the quasi-static model is labelled as a model on the page - CONFIRMED | Real losses happen in transients, in the moments as a basin finishes emptying or as other fixtures discharge into the same pipes. | https://nvlpubs.nist.gov/nistpubs/Legacy/BMS/nbsbuildingmaterialsstructures126.pdf (page image, PDF p. 17, p. 11; Foreword p. III) | "we are not interested in what happens in the trap when a steady state of flow has been established, but rather in what occurs under transient conditions, that is, when the discharge from the fixture ceases"; Foreword: fluctuations "which occur as the result of the discharge of the fixtures on the system" - CONFIRMED | The 1951 report that studied them called the problem | https://nvlpubs.nist.gov/nistpubs/Legacy/BMS/nbsbuildingmaterialsstructures126.pdf (page image, PDF p. 17, p. 11) | "we are concerned with an extremely complicated problem, one which defies analytical treatment." exact - CONFIRMED | and turned to experiments and dimensional analysis instead | https://nvlpubs.nist.gov/nistpubs/Legacy/BMS/nbsbuildingmaterialsstructures126.pdf (page image, PDF p. 17, p. 11) | "When a physical problem is too difficult for analytical treatment, one resource is to utilize dimensional analysis ... The experiments are then planned to develop this functional relation" - CONFIRMED | In the Bureau's plumbing report revised in 1928, R. B. Hunter and L. W. Snyder wrote | https://nvlpubs.nist.gov/nistpubs/Legacy/BH/nbsbuildinghousing13.pdf (PDF p. 78 and title page PDF p. 3) | chapter 6 head "By R. B. Hunter and L. W. Snyder Bureau of Standards"; title page "REVISED AUGUST 30, 1928" - CONFIRMED | An S or a P trap seal may be drawn to the point of breaking the seal with a loss of approximately one-half its full seal | https://nvlpubs.nist.gov/nistpubs/Legacy/BH/nbsbuildinghousing13.pdf (page image, PDF p. 157, p. 137) | read on the image: "An S or a P trap seal may be drawn to the point of breaking the seal with a loss of approximately one-half its full seal, after which it may be subjected repeatedly to the same or a smaller strain with no further loss of seal." The hyphen in one-half falls at a line end; the same paragraph prints "one-half" mid-line, so the transcription is right (OCR reads "onehalf") - CONFIRMED | Engineers at the US Bureau of Standards had already reported the same half. | https://nvlpubs.nist.gov/nistpubs/Legacy/BH/nbsbuildinghousing13.pdf (PDF p. 157, p. 137) | chapter 6 (PDF pp. 78 to 207) is Hunter and Snyder, Bureau of Standards; p. 137 reports the loss of "approximately one-half" and no further loss - CONFIRMED | Bureau of Standards engineers reported the same half in the 1920s | https://nvlpubs.nist.gov/nistpubs/Legacy/BH/nbsbuildinghousing13.pdf (p. 137); https://nvlpubs.nist.gov/nistpubs/Legacy/BMS/nbsbuildingmaterialsstructures126.pdf (pp. 7, 31) | BH13 revised 1928, p. 137; French and Eaton cite "[4, p. 137]" = BH2 (1924) for the one-half dividing line; either way the 1920s - CONFIRMED | In 1951 John French and Herbert Eaton gave the mechanism. | https://nvlpubs.nist.gov/nistpubs/Legacy/BMS/nbsbuildingmaterialsstructures126.pdf (title page image) | "John L. French and Herbert N. Eaton" - CONFIRMED | Let the room-side water fall to the dip, they wrote, and | https://nvlpubs.nist.gov/nistpubs/Legacy/BMS/nbsbuildingmaterialsstructures126.pdf (page image, PDF p. 13, p. 7) | preceded by "Now assume that a pressure reduction in the drain or other condition causes the water level in the inlet leg to fall until it just reaches the dip of the trap"; quotation exact - CONFIRMED | They named what is lost the critical trap-seal loss. | https://nvlpubs.nist.gov/nistpubs/Legacy/BMS/nbsbuildingmaterialsstructures126.pdf (PDF p. 13, p. 7) | "We propose the name, 'critical trap-seal loss,' for this condition." - CONFIRMED | they credit One investigator with proposing one half as the dividing line between satisfactory and unsatisfactory traps | https://nvlpubs.nist.gov/nistpubs/Legacy/BMS/nbsbuildingmaterialsstructures126.pdf (PDF p. 13, p. 7) | "One investigator [4, p. 137] has proposed that a value of 1/2 be used as the value of h/t to constitute the dividing line between satisfactory and unsatisfactory performance of the trap." - CONFIRMED | citing page 137 of the Bureau's 1924 Recommended minimum requirements for plumbing in dwellings and similar buildings | https://nvlpubs.nist.gov/nistpubs/Legacy/BMS/nbsbuildingmaterialsstructures126.pdf (page image, PDF p. 37, p. 31) | "[4] Recommended minimum requirements for plumbing in dwellings and similar buildings, Elimination of Waste Series, BH2, National Bureau of Standards (1924)." - CONFIRMED | the pressure they said would need studying was | https://nvlpubs.nist.gov/nistpubs/Legacy/BMS/nbsbuildingmaterialsstructures126.pdf (page image, PDF p. 37, p. 31) | "The latter method would require an investigation of the probability of a positive pressure equal in magnitude to twice the remaining trap seal occurring at the same time as the remaining trap seal in question." In the context of setting a requirement for remaining seals; quotation exact - CONFIRMED | The loss can go further if the suction | https://nvlpubs.nist.gov/nistpubs/Legacy/BMS/nbsbuildingmaterialsstructures126.pdf (PDF p. 13, p. 7) | "unless the pressure reduction in the drain becomes and remains for an appreciable length of time so excessive that air is sucked from the inlet leg ..." exact - CONFIRMED | carrying water with it by | https://nvlpubs.nist.gov/nistpubs/Legacy/BMS/nbsbuildingmaterialsstructures126.pdf (PDF p. 13, p. 7) | "carries with it some of the water in the trap by what may be called a pumping process." exact - CONFIRMED | French and Eaton worked out what that does for the five brass traps they tested | https://nvlpubs.nist.gov/nistpubs/Legacy/BMS/nbsbuildingmaterialsstructures126.pdf (PDF p. 13, p. 7, Table 1) | Table 1 "Dimensions of traps used in this investigation": five brass traps, figs. 7 to 11; "The traps investigated are shown in figures 7, 8, 9, 10, and 11" - CONFIRMED | simplified one step of the working by treating the two radii as equal | https://nvlpubs.nist.gov/nistpubs/Legacy/BMS/nbsbuildingmaterialsstructures126.pdf (PDF p. 13, p. 7) | "By making the assumption that these two radii are equal, a considerable simplification in the computations results, as will appear in the analysis to be given." exact; on p. 10 the assumption is used as Vb = Ve - CONFIRMED | The critical loss that comes out still keeps the two radii apart | https://nvlpubs.nist.gov/nistpubs/Legacy/BMS/nbsbuildingmaterialsstructures126.pdf (page image, PDF p. 16, p. 10) | print: "t-ru-ro, where ru is the radius of curvature of the the lower bend, and ro ... of the upper bend"; "Then hc=31/32÷2+1/2=0.985 inch", so hc = (t-ru-ro)/2 + ro keeps both radii. The record's excerpt writes "31/32/2" for the printed "31/32÷2" (finding 3) - CONFIRMED | They treated the outlet leg between the two bends as a cylinder | https://nvlpubs.nist.gov/nistpubs/Legacy/BMS/nbsbuildingmaterialsstructures126.pdf (PDF p. 16, p. 10) | "Vd is the volume of water contained in the cylindrical portion of the outlet leg of the trap, and hence the height of the cylinder occupied with the volume Vf is half the height of the cylindrical portion of the leg." - CONFIRMED | where ru is the radius of the lower bend and ro that of the upper one | https://nvlpubs.nist.gov/nistpubs/Legacy/BMS/nbsbuildingmaterialsstructures126.pdf (PDF p. 16, p. 10) | "where ru is the radius of curvature of the the lower bend, and ro is the radius of curvature of the upper bend (see fig. 12)" (the doubled "the" is in the print) - CONFIRMED | from the radii printed on their page 10 | https://nvlpubs.nist.gov/nistpubs/Legacy/BMS/nbsbuildingmaterialsstructures126.pdf (PDF p. 16, p. 10, read at 300 dpi) | all four rows read on the image: 2-17/32-1/2=31/32=0.969, hc 0.985; 3 3/16-15/16-13/16=1 7/16=1.437, hc 1.53; 1 3/4-17/32-11/32=7/8=0.875, hc 25/32=0.782; 3 9/16-17/16-25/32=1 23/32=1.697, hc 1 41/64=1.641. nbs1951.json and the verifier's typed fractions match every one - OBSERVED | so it loses 46.1% of its seal, not 50% | recreated: node -e "t=3+9/16;hc=(t-17/16-25/32)/2+25/32;console.log(hc,100*hc/t)" | 1.640625 in., 46.0526% -> 46.1%; ru - ro = 34/32 - 25/32 = 9/32 - OBSERVED | every computed row goes to exactly 50% | recreated: headless Chromium, page served from a scratch copy, button pressed | readout "every computed row is 50.0% of its seal: the formula is then exactly t/2"; (t-2r)/2 + r = t/2 - CONFIRMED | The fifth trap's 1.18 inches is French and Eaton's own estimate, from the volume of part of a torus | https://nvlpubs.nist.gov/nistpubs/Legacy/BMS/nbsbuildingmaterialsstructures126.pdf (page image, PDF p. 17, p. 11) | "equal to the volume of a torus having a central angle of about 30°" ... "the critical trap-seal loss is 1.18 inches"; water level 1.07 in. above the dip - CONFIRMED | on that trap's 2.25-inch seal it is 52.4% | https://nvlpubs.nist.gov/nistpubs/Legacy/BMS/nbsbuildingmaterialsstructures126.pdf (PDF p. 13 Table 1; PDF p. 16 fig. 11) | Table 1 "1 1/2-inch cast brass 2.25 1.50 1.50 11"; fig. 11 marks hc=1.18", zc=1.07"; 1.18/2.25 = 52.44% -> 52.4% - MINOR | computed 45% to 52% for five brass traps in 1951 | https://nvlpubs.nist.gov/nistpubs/Legacy/BMS/nbsbuildingmaterialsstructures126.pdf (pp. 7, 10, 11); recreated: node -e (printed hc / Table 1 t) | the numbers are right: from French and Eaton's printed losses (0.985, 1.53, 0.782, 1.641, 1.18 in.) on seals 2, 3 3/16, 1 3/4, 3 9/16, 2 1/4 the shares are 49.3%, 48.0%, 44.7%, 46.1%, 52.4% (recomputed rows 44.6% to 49.2%), so 45% to 52%. But BMS126 prints these losses in inches and gives no percentage for them; "computed 45% to 52%" credits them with this page's division (finding 2) - CONFIRMED | the print reads 1 23/32 inches = 1.697 inches | https://nvlpubs.nist.gov/nistpubs/Legacy/BMS/nbsbuildingmaterialsstructures126.pdf (PDF p. 16 at 300 dpi; shipped crop bms126-p10.png) | "t-ru-ro=3 9/16-17/16-25/32=1 23/32 inches=1.697 inches. Then hc=1.697/2+25/32=1 41/64 inches=1.641 inches." - OBSERVED | while 1.697 would have given 1.630 | recreated: node -e "console.log(1+23/32, 1.697/2+25/32, (1+23/32)/2+25/32, 1+41/64)" | 1.71875; 1.62975 -> 1.630; 1.640625 = 1 41/64 -> 1.641 - CONFIRMED | 25/32 inch is printed as 0.782 | https://nvlpubs.nist.gov/nistpubs/Legacy/BMS/nbsbuildingmaterialsstructures126.pdf (PDF p. 16 at 300 dpi) | "hc=(7/8)/2+11/32=25/32 inch=0.782." 25/32 = 0.78125 -> 0.781 - OBSERVED | None of this moves a share of the seal by as much as a tenth of a percentage point | recreated: node -e (abs(printed/t - exact/t) x 100 for the four rows) | 0.031, 0.039, 0.043, 0.011 percentage points; all under 0.1 - OBSERVED | the scan's machine-read text garbles these fractions | recreated: pdftotext -layout -f 16 -l 16 nbsbuildingmaterialsstructures126.pdf | OCR gives "2 ^%2 /'2 ^K2", "3%6-'K6-iK6=lK6", "{%)n + ')i2 = ^%2" for the printed fractions - CONFIRMED | A US Government work (no US copyright). | https://www.law.cornell.edu/uscode/text/17/105 | "Copyright protection under this title is not available for any work of the United States Government"; BMS126 is an NBS report (title page) - CONFIRMED | The 1961 Bureau monograph on drainage stacks puts the cause in two sentences | https://nvlpubs.nist.gov/nistpubs/Legacy/MONO/nbsmonograph31.pdf (title page image, PDF p. 3) | "Capacities of Stacks in Sanitary Drainage Systems for Buildings", "National Bureau of Standards Monograph 31", "Issued July 3, 1961" - CONFIRMED | The friction thus developed drags air along with the water. | https://nvlpubs.nist.gov/nistpubs/Legacy/MONO/nbsmonograph31.pdf (page image, PDF p. 23, p. 19) | section 4.4 Air Flow in Drainage Systems; both sentences exact on the image (OCR interleaves "en-closes") - CONFIRMED | Hunter and Snyder had mapped the result with pressure gauges up and down their test stacks | https://nvlpubs.nist.gov/nistpubs/Legacy/BH/nbsbuildinghousing13.pdf (page image, PDF p. 130, p. 110) | "Numerous air-pressure measurements were made with sensitive pressure gauges at various points from the base of the stack upward in the plumbing test installations used." - CONFIRMED | In all cases back pressures only were encountered at the base of the stack. | https://nvlpubs.nist.gov/nistpubs/Legacy/BH/nbsbuildinghousing13.pdf (page image, PDF p. 130, p. 110) | four sentences exact on the image ("all", not the OCR's "ail") - CONFIRMED | the 1961 monograph agrees on the two ends | https://nvlpubs.nist.gov/nistpubs/Legacy/MONO/nbsmonograph31.pdf (page image, PDF p. 43, p. 39, section 7.5c) | both sentences exact - CONFIRMED | Its own discharge can pull its own seal down: the 1951 report calls that self-siphonage. | https://nvlpubs.nist.gov/nistpubs/Legacy/BMS/nbsbuildingmaterialsstructures126.pdf (Foreword, PDF p. 5) | "Self-siphonage is the reduction in the water seal of a fixture trap by the discharge from the fixture to which the trap is connected." app.mjs text seen at load in headless Chromium - CONFIRMED | Just below the inflow: partial vacuum. | https://nvlpubs.nist.gov/nistpubs/Legacy/MONO/nbsmonograph31.pdf (p. 39); https://nvlpubs.nist.gov/nistpubs/Legacy/BH/nbsbuildinghousing13.pdf (p. 110) | "Least pressures occur immediately below a point of water entrance"; Hunter and Snyder: "In the upper portions of the stack below the entrance point of the discharge partial vacuums only were encountered." Readout seen at load - CONFIRMED | At the base of the stack: back pressure. | https://nvlpubs.nist.gov/nistpubs/Legacy/BH/nbsbuildinghousing13.pdf (p. 110) | "In all cases back pressures only were encountered at the base of the stack." Readout seen in headless Chromium (inflow 8, trap at base) - CONFIRMED | Hunter and Snyder found partial vacuum in the upper part of this stretch, back pressure in the lower part, and an alternating region between, with the back-pressure region reaching higher as the flow grew | https://nvlpubs.nist.gov/nistpubs/Legacy/BH/nbsbuildinghousing13.pdf (p. 110) | all four sentences of the p. 110 passage; attributed to Hunter and Snyder only, correctly (Monograph 31 p. 29 found the zero point "fairly definite" in its own stack-vented tests) - CONFIRMED | With the stack top open, Hunter and Snyder found no measurable effect at points above the inlet. | https://nvlpubs.nist.gov/nistpubs/Legacy/BH/nbsbuildinghousing13.pdf (page image, PDF p. 175, p. 155) | "at points on the stack above the inlet through which water was introduced into the stack showed no measurable effects when the stack top was open." - CONFIRMED | In the stack at the level of the inflow, with the stack top open, Hunter and Snyder found only very slight suctions or back pressures. | https://nvlpubs.nist.gov/nistpubs/Legacy/BH/nbsbuildinghousing13.pdf (page image, PDF p. 175, p. 155) | "At the same level as the inflow only very slight suctions or back pressures were produced." (the next sentence of the same report, in the crowfoot-fitting discussion; the open-top condition carries over from the sentence before) - CONFIRMED | no measurable effect above the inflow, very slight at it (stack top open) | https://nvlpubs.nist.gov/nistpubs/Legacy/BH/nbsbuildinghousing13.pdf (p. 155) | the two sentences above; legend text checked in the HTML - CONFIRMED | The signs are for a branch with no vent of its own. | https://nvlpubs.nist.gov/nistpubs/Legacy/BH/nbsbuildinghousing13.pdf (p. 110) | "These pressures, especially the partial vacuums, are not necessarily those in the center of the stack, but rather the pressures that would be produced in an unvented branch line connecting at that point." - CONFIRMED | For a 3-inch stack vented only through its open top, Hunter and Snyder noted that their readings were | https://nvlpubs.nist.gov/nistpubs/Legacy/BH/nbsbuildinghousing13.pdf (p. 110) | "Figures 42 and 43 illustrate the pressure effects in a 3-inch stack, unvented except by the open stack top." - CONFIRMED | Hunter and Snyder noted that their readings were | https://nvlpubs.nist.gov/nistpubs/Legacy/BH/nbsbuildinghousing13.pdf (p. 110) | quotation exact on the image - CONFIRMED | And their measurements at points on the stack | https://nvlpubs.nist.gov/nistpubs/Legacy/BH/nbsbuildinghousing13.pdf (p. 155) | quotation exact on the image - CONFIRMED | a 3-inch stack 33 feet long, vented only through its open top, took water at 200 gallons a minute | https://nvlpubs.nist.gov/nistpubs/Legacy/BH/nbsbuildinghousing13.pdf (page image, PDF p. 134, p. 114) | "With the 3-inch stack 33 feet long (fig. 46) unvented except through the open top water was introduced through a P trap and Y fitting at the rate of 200 gallons per minute" - CONFIRMED | In one of Hunter and Snyder's tests | https://nvlpubs.nist.gov/nistpubs/Legacy/BH/nbsbuildinghousing13.pdf (p. 114) | "The maximum of any individual pressure reading was 31.3 inches of water vacuum at the point 10 inches below the entrance point." exact (OCR interleaves the next sentence) - OBSERVED | That is more than fifteen times the suction a full 2-inch seal can take. | recreated: 31.3 / 2 = 15.65 | more than fifteen times a full 2-inch seal's suction limit in the model (t) - CONFIRMED | Hunter and Snyder worked out vent sizes from the assumption | https://nvlpubs.nist.gov/nistpubs/Legacy/BH/nbsbuildinghousing13.pdf (p. 114; p. 112 for context) | p. 112: "possible to calculate the requirements in sizes of vents ... provided a starting point for the calculation is given"; p. 114: "This starting point we have established on the following assumptions: ... (3) that no positive or back pressure greater than 1 inch ..." exact - CONFIRMED | In 1961 the monograph described the vent tables in most plumbing codes as meant to keep pressures at critical points within plus or minus 1 inch of water column | https://nvlpubs.nist.gov/nistpubs/Legacy/MONO/nbsmonograph31.pdf (page image, PDF p. 24, p. 20) | "In most plumbing codes a loading table for vents is provided. The purpose of such a table is to give the information necessary to design the vent stack ... for the control of pneumatic pressures at critical points in the drainage system within limits of +1 to -1 in. of water column from atmospheric." - CONFIRMED | within plus or minus 1 inch of water column, and added | https://nvlpubs.nist.gov/nistpubs/Legacy/MONO/nbsmonograph31.pdf (p. 20) | exact on the image ("fixture-trap seals"); OCR splits it across a figure caption - OBSERVED | In the model, a 2-inch seal pulled by 1 inch keeps 1.5 inches, and then needs 3 inches of back pressure before sewer air bubbles through. | recreated: afterSuction(2,2,1) = 1.5; backBreak(2,1.5) = 3 | labelled "In the model" on the page - CONFIRMED | England's Approved Document H states its rule as a seal kept, not a pressure | https://assets.publishing.service.gov.uk/media/5a80cf9ded915d74e33fc8ae/BR_PDF_AD_H_2015.pdf (p. 6, para 1.3) | "Under working and test conditions traps should retain a minimum seal of 25mm of water or equivalent." exact - CONFIRMED | Hunter and Snyder's test logs name what they saw in words like these | https://nvlpubs.nist.gov/nistpubs/Legacy/BH/nbsbuildinghousing13.pdf (page image, PDF p. 191, p. 171, note to series 2 tables) | "'Blown' means water thrown up from the closet bowl or out of the bowl by back pressure." exact - CONFIRMED | Bubble or bubbles, which means a small quantity of air | https://nvlpubs.nist.gov/nistpubs/Legacy/BH/nbsbuildinghousing13.pdf (p. 171) | "'Bubble' or 'bubbles' means a small quantity of air forced back through the trap by back pressure." exact - CONFIRMED | The 1951 foreword joined the two halves of this page in one sentence | https://nvlpubs.nist.gov/nistpubs/Legacy/BMS/nbsbuildingmaterialsstructures126.pdf (Foreword image at 300 dpi, PDF p. 5) | exact; the image has no comma after "system" (the OCR adds one) - CONFIRMED | The 1928 committee already counted it among the reasons a seal needs a margin | https://nvlpubs.nist.gov/nistpubs/Legacy/BH/nbsbuildinghousing13.pdf (page image, PDF p. 72, p. 54, chapter 5, the committee's text) | "some factor of safety must be allowed to provide for unexpected shocks, for evaporation, capillary loss, and for oscillations due to wind pressure" exact - CONFIRMED | J. J. Cosgrove's Principles and Practice of Plumbing (1906), working from experiments by a Dr. Unna, municipal engineer of Cologne, gave a rule for unvented traps | https://archive.org/download/principlespracti00cosguoft/page/n56_w1200.jpg (p. 45 image) | headed Evaporation of Water from Traps: "From experiments made by Dr. Unna, Municipal Engineer of Cologne"; title page "By J. J. COSGROVE"; copyright 1906 - CONFIRMED | gave a rule for unvented traps | https://archive.org/download/principlespracti00cosguoft/page/n56_w1200.jpg (p. 45 image) | exact on the page image - CONFIRMED | For vented traps he had no data, but thought | https://archive.org/download/principlespracti00cosguoft/page/n56_w1200.jpg (p. 45 image) | "No experimental data is available to show the rate of evaporation of water from ventilated traps, but it would be safe to assume a rate of .8 of an inch per week." exact - CONFIRMED | His own worked example, a 1¾-inch seal destroyed | https://archive.org/download/principlespracti00cosguoft/page/n56_w1200.jpg (p. 45 image) | "an unvented siphon trap with a 1 3/4-inch depth of seal will be destroyed in from four and a half to five weeks' time" (image shows 1¾) - OBSERVED | implies 0.35 to 0.39 inch a week | recreated: 1.75/5 = 0.35; 1.75/4.5 = 0.389 | 0.35 to 0.39 inch a week - OBSERVED | The slider starts at his 0.4 inch, which is 10.16 mm, a week | recreated: 0.4 x 25.4 = 10.16; index.html slider value="10.16"; readout at load "10.16 (0.400 in.)" | matches - CONFIRMED | put the risk in one sentence, in a practice note first issued in June 2003 | https://www.bd.gov.hk/doc/en/resources/codes-and-references/practice-notes-and-circular-letters/pnap/ADV/ADV024.pdf | "First issue June 2003 (AD/NB1)" - CONFIRMED | quoted here from its re-issue of August 2009 | https://www.bd.gov.hk/doc/en/resources/codes-and-references/practice-notes-and-circular-letters/pnap/ADV/ADV024.pdf | "Re-issued under new categorization in August 2009 as Practice Note for Authorized Persons, Registered Structural Engineers and Registered Geotechnical Engineers" - CONFIRMED | put the risk in one sentence | https://www.bd.gov.hk/doc/en/resources/codes-and-references/practice-notes-and-circular-letters/pnap/ADV/ADV024.pdf | para 1, exact - CONFIRMED | The Amoy Gardens reports give no figure for how far the fans pulled | https://www.info.gov.hk/info/sars/pdf/amoy_e.pdf; https://www.info.gov.hk/info/sars/who-amoye.pdf | both read in full: no fan pressure figure in either - CONFIRMED | SARS broke out among the residents of Amoy Gardens, a private housing estate in Kowloon Bay, Hong Kong, towards the end of March 2003. | https://www.info.gov.hk/info/sars/pdf/amoy_e.pdf; https://www.sars-expertcom.gov.hk/english/reports/reports/files/e_chp3_23.pdf | DoH: "occurred among residents of Amoy Gardens, Kowloon Bay, towards the end of March 2003"; Expert Committee 3.69: "Amoy Gardens, a private housing estate built in 1981" - CONFIRMED | By the Department of Health's count | https://www.info.gov.hk/info/sars/pdf/amoy_e.pdf (para 3) | exact - CONFIRMED | Block E held 41% of them. | https://www.info.gov.hk/info/sars/pdf/amoy_e.pdf (para 3) | "There was an obvious concentration of cases in Block E, accounting for 41% of the cumulative total." - CONFIRMED | Hong Kong's SARS Expert Committee later gave the final toll | https://www.sars-expertcom.gov.hk/english/reports/reports/files/e_chp3_23.pdf (para 3.67) | exact - CONFIRMED | The blocks were plumbed the way this page has been describing. | https://www.info.gov.hk/info/sars/pdf/amoy_e.pdf (para 7) | both sentences exact - CONFIRMED | Each of those fixtures had a U-trap | https://www.info.gov.hk/info/sars/pdf/amoy_e.pdf (para 7) | "Each of these sanitary fixtures is fitted with a U-shaped water trap (U-trap)" - CONFIRMED | the Department's report of 17 April 2003 set down the condition in one line | https://www.info.gov.hk/info/sars/pdf/amoy_e.pdf (para 7) | exact; report signed "Department of Health 17 April 2003" - CONFIRMED | The Department reasoned that the toilets, basins and baths were used often enough to keep their traps charged | https://www.info.gov.hk/info/sars/pdf/amoy_e.pdf (para 8) | "As the water closets, the basins and the bathtubs were frequently used, their U-traps should be charged with water and should have been functioning properly." - CONFIRMED | but that the floor drains were another matter | https://www.info.gov.hk/info/sars/pdf/amoy_e.pdf (para 8) | exact - CONFIRMED | Likely, not measured: the report gives no seal depths. | https://www.info.gov.hk/info/sars/pdf/amoy_e.pdf | six pages read in full: "likely to be dry"; no seal depth anywhere - CONFIRMED | A test in one Block E flat showed what such a drain does | https://www.info.gov.hk/info/sars/pdf/amoy_e.pdf (para 8) | "Indeed, in tests carried out in one of the units in Block E, reflux of air ... was demonstrated when the exhaust fan in the bathroom was switched on." exact - CONFIRMED | the Department wrote | https://www.info.gov.hk/info/sars/pdf/amoy_e.pdf | heading above paras 12 to 16, exact - CONFIRMED | The bathroom floor drains with dried-up U-traps provided a pathway | https://www.info.gov.hk/info/sars/pdf/amoy_e.pdf (para 15) | both sentences exact - CONFIRMED | A month later an independent WHO environmental health team reached a similar view | https://www.healthbureau.gov.hk/en/press_and_publications/press/2003/press030516a.htm | "The Government today (May 16) welcomed the findings of an independent investigation ... conducted by the Environmental Health Team of the World Health Organisation (WHO)"; "the WHO team reached similar conclusions through an independent exercise" - CONFIRMED | In the case of a running exhaust fan and a closed door | https://www.info.gov.hk/info/sars/who-amoye.pdf (Conclusions) | three sentences exact - CONFIRMED | The Department's probable explanation also names | https://www.info.gov.hk/info/sars/pdf/amoy_e.pdf (para 14, under the same heading) | exact - CONFIRMED | The WHO team's concluding remark reads | https://www.info.gov.hk/info/sars/who-amoye.pdf (Concluding remark) | exact - CONFIRMED | The Government's press release that day reported the Deputy Director of Health, Dr Leung Pak-yin | https://www.healthbureau.gov.hk/en/press_and_publications/press/2003/press030516a.htm | "Speaking at a press conference, the Deputy Director of Health, Dr Leung Pak-yin, said"; dated "End/Friday, May 16, 2003" - CONFIRMED | noting that both investigations pointed to | https://www.healthbureau.gov.hk/en/press_and_publications/press/2003/press030516a.htm | "Dr Leung noted that both the findings of the WHO and the Department of Health indicated that the outbreak at Amoy Gardens was highly likely to be caused by a combination of events." - CONFIRMED | Airborne? The Department of Health, 17 April 2003 | https://www.info.gov.hk/info/sars/pdf/amoy_e.pdf (para 16) | exact - CONFIRMED | The same report postulates that droplets from the soil stack, drawn by bathroom exhaust fans into the light well | https://www.info.gov.hk/info/sars/pdf/amoy_e.pdf (para 8) | "It is postulated that the reflux could have contained droplets ... be extracted by the bathroom exhaust fan into the light well between adjacent units." - CONFIRMED | drawn by bathroom exhaust fans into the light well, | https://www.info.gov.hk/info/sars/pdf/amoy_e.pdf (para 8, across the p. 2/3 break) | "The contaminated droplets could then enter other units through open windows." exact - CONFIRMED | Airborne? Yu and colleagues, New England Journal of Medicine, 2004 | https://eutils.ncbi.nlm.nih.gov/entrez/eutils/efetch.fcgi?db=pubmed&id=15102999&rettype=abstract&retmode=text | BACKGROUND, exact - CONFIRMED | and concluded | https://eutils.ncbi.nlm.nih.gov/entrez/eutils/efetch.fcgi?db=pubmed&id=15102999&rettype=abstract&retmode=text | CONCLUSIONS, exact - CONFIRMED | Tests found a large crack in a sewer vent pipe at the fourth floor of Block E. | https://www.info.gov.hk/info/sars/pdf/amoy_e.pdf (paras 9, 20) | "other tests detected leakage from a sewer vent pipe at the 4/F of Block E, and was confirmed by a large visible crack." - CONFIRMED | The cracked vent pipe: the Department of Health | https://www.info.gov.hk/info/sars/pdf/amoy_e.pdf (para 9) | exact - CONFIRMED | The broken vent pipe: the WHO team | https://www.info.gov.hk/info/sars/who-amoye.pdf (Results) | exact - CONFIRMED | Neither report says whether the two describe the same pipe. | https://www.info.gov.hk/info/sars/who-amoye.pdf; https://www.info.gov.hk/info/sars/pdf/amoy_e.pdf | both read in full: WHO "the broken vent pipe discovered at the bottom of the light well"; DoH "a sewer vent pipe at the 4/F of Block E"; neither links the two - CONFIRMED | in the Department's own test a running exhaust fan drew air from the soil stack up through a floor drain | https://www.info.gov.hk/info/sars/pdf/amoy_e.pdf (para 8) | "reflux of air from the soil stack into the bathroom through the floor drain was demonstrated when the exhaust fan in the bathroom was switched on" - CONFIRMED | when a team in Guangzhou investigated nine people infected with SARS-CoV-2, in three families who lived in vertically aligned flats connected by drainage pipes | https://eutils.ncbi.nlm.nih.gov/entrez/eutils/efetch.fcgi?db=pubmed&id=32870707&rettype=abstract&retmode=text | "9 infected patients in 3 families were identified"; "The families lived in 3 vertically aligned flats connected by drainage pipes in the master bathrooms"; SETTING "A high-rise apartment building in Guangzhou, China"; Ann Intern Med 2020 - CONFIRMED | Their abstract lists as a limitation the | https://eutils.ncbi.nlm.nih.gov/entrez/eutils/efetch.fcgi?db=pubmed&id=32870707&rettype=abstract&retmode=text | "LIMITATION: Inability to determine whether the water seals were dried out in the flats of the infected families." exact - CONFIRMED | Part of the advice that followed Amoy Gardens was plain plumbing | https://www.info.gov.hk/info/sars/pdf/amoy_e.pdf (para 19) | "Residents of Amoy Gardens were advised to ensure the water level at the U-traps of drainage outlets to ensure proper functioning." - CONFIRMED | the Buildings Department suggested that building designers consider diverting some waste water from another fitting into the floor-drain trap | https://www.bd.gov.hk/doc/en/resources/codes-and-references/practice-notes-and-circular-letters/pnap/ADV/ADV024.pdf (para 2) | "To obviate the need to top up the water in the trap of floor drains ... authorized persons (APs) may wish to consider diverting some of the waste water from a waste fitment to the U-trap of floor drains in their designs." - CONFIRMED | the seal failure that both official accounts point to at Amoy Gardens needed no pressure at all, only long periods without water | https://www.info.gov.hk/info/sars/who-amoye.pdf; https://www.info.gov.hk/info/sars/pdf/amoy_e.pdf | WHO: "seemed to have not been filled with water for long periods"; DoH: "dried-up U-traps", "likely to be dry" from mopping - CONFIRMED | The Amoy Gardens reports give no fan pressures and no seal depths, and this page invents neither. | https://www.info.gov.hk/info/sars/pdf/amoy_e.pdf; https://www.info.gov.hk/info/sars/who-amoye.pdf | both read in full: no fan pressure and no seal depth - OBSERVED | Quotations are verbatim; for the scanned reports they were read from the page images. | recreated: every quotation from BMS126, Monograph 31, BH13 and Cosgrove read against page images rendered from the live PDFs (byte-identical to the builder's, sha256 checked) and archive.org page 45 | all verbatim; the OCR differs ("ail", "onehalf", the extra comma, interleaved columns), the page does not - CONFIRMED | Recommended Minimum Requirements for Plumbing, revised August 30, 1928 (Bureau of Standards; Government Printing Office, 1929), including chapter 6 by R. B. Hunter and L. W. Snyder | https://nvlpubs.nist.gov/nistpubs/Legacy/BH/nbsbuildinghousing13.pdf (title page image) | "RECOMMENDED MINIMUM REQUIREMENTS FOR PLUMBING ... SUBCOMMITTEE ON PLUMBING OF THE BUILDING CODE COMMITTEE REVISED AUGUST 30, 1928 ... R. B. HUNTER, In Charge of Tests BUREAU OF STANDARDS ... GOVERNMENT PRINTING OFFICE WASHINGTON 1929"; chapter 6 by Hunter and Snyder - CONFIRMED | J. L. French and H. N. Eaton, Self-Siphonage of Fixture Traps, NBS Building Materials and Structures Report BMS126, issued October 15, 1951 | https://nvlpubs.nist.gov/nistpubs/Legacy/BMS/nbsbuildingmaterialsstructures126.pdf (title page image) | title, authors, "Building Materials and Structures Report 126", "Issued October 15, 1951" - CONFIRMED | R. S. Wyly and H. N. Eaton, Capacities of Stacks in Sanitary Drainage Systems for Buildings, NBS Monograph 31, issued July 3, 1961 | https://nvlpubs.nist.gov/nistpubs/Legacy/MONO/nbsmonograph31.pdf (title page image) | "Robert S. Wyly and Herbert N. Eaton", "Monograph 31", "Issued July 3, 1961" - CONFIRMED | J. J. Cosgrove, Principles and Practice of Plumbing (Pittsburgh: Standard Sanitary Mfg. Co., 1906) | https://archive.org/download/principlespracti00cosguoft/page/n7_w1200.jpg | copyright page image: "Copyright 1906 by Standard Sanitary Mfg. Co. Pittsburgh, U. S. A." - CONFIRMED | Standard Sanitary Mfg. Co., 1906). Public domain. | https://archive.org/metadata/principlespracti00cosguoft | "possible-copyright-status":"NOT_IN_COPYRIGHT"; US publication of 1906 - CONFIRMED | HM Government, Approved Document H: Drainage and waste disposal, 2015 edition, paragraph 1.3 and Table 1. Crown copyright, Open Government Licence v3.0. | https://assets.publishing.service.gov.uk/media/5a80cf9ded915d74e33fc8ae/BR_PDF_AD_H_2015.pdf (cover; p. 6; licence page) | cover "HM Government ... Drainage and waste disposal ... 2015 edition"; "© Crown Copyright, 2015 ... under the terms of the Open Government Licence v3." - CONFIRMED | NIST Guide to the SI, Appendix B.8: Factors for Units Listed Alphabetically (millimeter of water, conventional). | https://www.nist.gov/pml/special-publication-811/nist-guide-si-appendix-b-conversion-factors/nist-guide-si-appendix-b8 | page title "NIST Guide to the SI, Appendix B.8: Factors for Units Listed Alphabetically" - CONFIRMED | Outbreak of Severe Acute Respiratory Syndrome (SARS) at Amoy Gardens, Kowloon Bay, Hong Kong: Main Findings of the Investigation, 17 April 2003. Copyright Government of the Hong Kong SAR | https://www.info.gov.hk/info/sars/pdf/amoy_e.pdf; https://www.info.gov.hk/info/sars/en/notice.htm | title exact; signed 17 April 2003; notice: "subject to copyright owned by the Government of the Hong Kong Special Administrative Region" - CONFIRMED | WHO Regional Office for the Western Pacific, Environmental Health Team report on Amoy Gardens, released 16 May 2003, hosted by the Hong Kong Government | https://www.info.gov.hk/info/sars/en/report.htm; https://www.info.gov.hk/info/sars/who-amoye.pdf | index "WHO Environmental Health Team Reports on Amoy Gardens (16.5.2003)"; report header "WORLD HEALTH ORGANIZATION REGIONAL OFFICE FOR THE WESTERN PACIFIC" - CONFIRMED | Hong Kong Government press release, WHO investigation findings support HK's work, 16 May 2003. | https://www.healthbureau.gov.hk/en/press_and_publications/press/2003/press030516a.htm | headline "WHO investigation findings support HK's work"; "End/Friday, May 16, 2003" - CONFIRMED | SARS Expert Committee, SARS in Hong Kong: from Experience to Action, chapter 3, The SARS Epidemic, section The Community Outbreak in Amoy Gardens. | https://www.sars-expertcom.gov.hk/english/reports/reports/files/e_chp3_23.pdf | running title "SARS in Hong Kong: from Experience to Action"; chapter 3 "The SARS Epidemic"; section "The Community Outbreak in Amoy Gardens" - CONFIRMED | Buildings Department, Hong Kong, Practice Note ADV-24, Floor Drains in Kitchens and Bathrooms, first issued June 2003; quoted briefly from the re-issue of August 2009. | https://www.bd.gov.hk/doc/en/resources/codes-and-references/practice-notes-and-circular-letters/pnap/ADV/ADV024.pdf | title "Floor Drains in Kitchens and Bathrooms", "ADV-24", first issue June 2003, re-issued August 2009 - CONFIRMED | I. T. Yu and others, Evidence of airborne transmission of the severe acute respiratory syndrome virus, New England Journal of Medicine 350 (2004), 1731–1739 | https://eutils.ncbi.nlm.nih.gov/entrez/eutils/efetch.fcgi?db=pubmed&id=15102999&rettype=abstract&retmode=text; https://api.crossref.org/works/10.1056/NEJMoa032867 | N Engl J Med 2004;350(17):1731-9; Crossref volume 350, page 1731-1739; first author Yu (Crossref "Ignatius T.S.", PubMed "Yu IT") - CONFIRMED | M. Kang and others, Probable Evidence of Fecal Aerosol Transmission of SARS-CoV-2 in a High-Rise Building, Annals of Internal Medicine 173 (2020), 974–980 | https://eutils.ncbi.nlm.nih.gov/entrez/eutils/efetch.fcgi?db=pubmed&id=32870707&rettype=abstract&retmode=text; https://api.crossref.org/works/10.7326/M20-0928 | Ann Intern Med 2020;173(12):974-980; Crossref agrees; first author Min Kang - CONFIRMED | A hard suction from the drain can pull out about half of that water | https://nvlpubs.nist.gov/nistpubs/Legacy/BH/nbsbuildinghousing13.pdf (p. 137) | "with a loss of approximately one-half its full seal" - CONFIRMED | in 2003 dry floor drains in a Hong Kong housing estate were judged a probable route for the SARS virus | https://www.info.gov.hk/info/sars/pdf/amoy_e.pdf (paras 12 to 15) | under "PROBABLE EXPLANATION OF THE OUTBREAK": "The bathroom floor drains with dried-up U-traps provided a pathway" - OBSERVED | each figure on this page is either computed or taken from a named source | recreated: node $SP/wave-sweep.mjs the-water-between-you-and-the-sewer --jobs 2 (240 mutated, 240 caught, 0 survived) and the plain run (residual sweep passes) | every numeric token is computed, sourced or declared - WRONG | (added) With --mutate it plants one wrong figure in a copy of the page and must fail. | verify-the-water-between-you-and-the-sewer.mjs lines 513-531; recreated: AW_DIR= node verify-the-water-between-you-and-the-sewer.mjs --mutate | the mutant plants six figures in the page at once (981 Pa to 918, 46.1% to 47.1%, "41% of them, in 33 storeys", 0.782 to 0.783, 3-inch to 4-inch, 1955 to 1956) and one in nbs1951.json (row 3 r_o to 13/32); the run printed "8 checks failed on the mutant" (finding 1) - OBSERVED | (added) the check section: it downloads index.html, engine.mjs, nbs1951.json and quotes.json; steps the water on a grid with its own bookkeeping; recomputes four traps, checks the fifth and the two slips; recomputes units and evaporation; finds every figure in its sentence; checks quotations and the head copies | recreated: verifier copied to an empty directory, AW_DIR pointing at a second holding only those four files: exit 0, 290 passed, 0 failed; FILES = the four names; sections A to E as described | matches - CONFIRMED | (added) Every sink, bath, shower and floor drain reaches the sewer through a pipe that dips and rises again, and the dip keeps water. | https://assets.publishing.service.gov.uk/media/5a80cf9ded915d74e33fc8ae/BR_PDF_AD_H_2015.pdf (para 1.3); https://www.bd.gov.hk/doc/en/resources/codes-and-references/practice-notes-and-circular-letters/pnap/ADV/ADV024.pdf (para 1) | AD H: "All points of discharge into the system should be fitted with a trap (e.g. a water seal trap)"; ADV-24: "Water seal traps are required to be provided for all sanitary fitments, including floor drains (if provided)". True of plumbing built to these codes - CONFIRMED | (added) The map is only signs, because these sources give no general rule for where one region ends. | https://nvlpubs.nist.gov/nistpubs/Legacy/MONO/nbsmonograph31.pdf (pp. 29, 39); https://nvlpubs.nist.gov/nistpubs/Legacy/BH/nbsbuildinghousing13.pdf (p. 110) | Monograph 31 p. 29: the pressure "tended to approach atmospheric at a fairly definite point" in its own stack-vented tests, but "The elevation of the point of atmospheric pressure is affected by the resistance to flow ... offered by the building drain"; no general rule is given - CONFIRMED | (added) relates: chimney-stack-effect, water-under-tension, the-average-that-hides-the-outbreak, coriolis-drain, with their notes | src/content/strata/.md | all four exist; each note matches that layer's dek (column-weight draft; 10.33 m atmosphere ceiling; dispersion k and a fitted SARS estimate; basin swirl not set by hemisphere) - CONFIRMED | (added) French and Eaton, NBS BMS126, page 10, as printed (the shipped crop bms126-p10.png) | https://nvlpubs.nist.gov/nistpubs/Legacy/BMS/nbsbuildingmaterialsstructures126.pdf (PDF p. 16 rendered at 300 dpi) | the crop is an unaltered piece of p. 10 (from "the lower bend" to "1 1/2 inch cast brass trap (see fig. 11)"); its alt text names the same printed figures - OBSERVED | (added) The trap drawings and the stack map are this page's own; no figure from the Hong Kong reports is reproduced. | recreated: grep -n "