Core TradesQuestion 85 of 700
A fixture drain is located far from any vent, and after installation the trap seals siphon out, letting sewer gas into the room. The MOST likely code violation is:
a.The trap is too large
b.The trap arm exceeds the maximum developed length allowed to its vent
c.The pipe slope is too steep
d.The fixture is too close to the stack
Explanation
When the trap arm (horizontal distance from trap to vent) exceeds the code maximum for its pipe size, the trap can self-siphon and lose its seal, admitting sewer gas. Trap size, moderate slope, and closeness to the stack are not what causes siphonage from an over-long trap arm.
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