Your Sink Is Never Empty

Why is there always water in the bend under your sink? That water is a seal: it keeps the air from the sewer out of your room.

In 1775 the watchmaker Alexander Cumming patented a water closet built around an S-shaped bend, and his patent calls it the “stink trap”. Today New York City’s plumbing code asks for two to four inches of water in every fixture trap, and England’s building regulations ask for at least 75 mm under a sink or basin. Leave a drain unused long enough and that water evaporates, which is why a home left empty can smell of sewer.

The opening shot (0:00–0:03) is an AI-generated image. Every other frame is a real photo, real footage or our own diagram.

Sources:
The National Archives (UK), “Innovations in toilet design” (Cumming’s patent no. 1105, 1775):
New York City Plumbing Code 2022, Section PC 1002.4, Trap seals:
Approved Document H: Drainage and waste disposal, 2015 edition (England), para 1.3 and Table 1:
South Davis Sewer District, “What’s That Smell? Understanding Sewer Odors and P-Traps” (19 Jan 2026):

Photos, via Wikimedia Commons:
Brass P-trap: Raquel Baranow, CC BY-SA 4.0,
Chrome P-trap under a basin: mariemon, CC BY 3.0,
S-shaped trap: VanBuren, CC BY-SA 3.0,
PVC J-bend: Steven Pavlov, CC0,

Photos and footage via Pexels: Liliana Drew (sink drain), Jordan Besson (tunnel), Nitin Chauhan (empty room).

#plumbing #howthingswork

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