trap seal การใช้

Generally, a toilet outlet has the shortest trap seal, making it most vulnerable to being emptied by induced siphonage.
On the other hand, if the air pressure within the drain becomes suddenly higher than ambient, this positive transient could cause waste water to be pushed into the fixture, breaking the trap seal, with serious hygiene and health consequences if too forceful.
:: Our article on drain-waste-vent system says " Excessive negative air pressure, behind a'slug'of water that is draining, can siphon water from trap seals at plumbing fixtures . . . . An empty trap can allow noxious sewer gasses to enter a building ".