P-Trap

trap (or water seal) keeps sewer gases from emanating out of the drainage system. A trap is a simple U-shaped pipe arrangement. The shape offers minimal resistance to the flow. The water seal prevents sewer gases and airborne bacteria from entering the interior air of the building. The only type of fixture trap permitted is the P-trap. All other types, including bell traps, drum traps, S-traps, and traps with moving parts, are prohibited. Traps shall have a water seal of at least 2 inches and, at most, 4 inches in depth. Traps for floor drains should be fitted with a trap primer or should be of the deep-seal design. Traps should be level with respect to the water seal. Traps should be protected from freezing. Trap seals should be protected from siphonage, aspiration, and back-pressure by an approved venting system.