Bottle Traps, P Traps & S Traps
The trap holds a water seal that stops foul air from the drainage system entering the room. It is the single most important small component in the system, and the one most often defeated by poor branch design.
Also searched as: bottle trap, P trap, S trap, water seal, basin trap, sink trap, deep seal trap
Types
Bottle trap — compact and neat, used under exposed basin wastes where appearance matters. P trap — horizontal outlet, the standard for a wall connection. S trap — vertical outlet, for a connection dropping straight through the floor. Shallow-seal and low-level patterns are available for shower trays and for restricted voids.
Seal depth
A 75mm deep seal is the normal specification and is what should be used on any run that might be subject to pressure fluctuation — which in a high-rise tower means effectively all of them. A 38mm shallow seal is only appropriate where the branch is short, correctly vented and the appliance is in constant use.
Why seals are lost
Self-siphonage from an over-long or over-steep branch, induced siphonage from another appliance discharging, back-pressure at the foot of a stack, and simple evaporation in an unused room during the Gulf summer. The first three are design problems and are addressed in the branch and stack rules in the Technical Manual.