Core TradesQuestion 190 of 700
Why does the plumbing code prohibit the use of an 'S-trap' on a fixture?
a.It is too expensive to install
b.It requires a larger cleanout than a P-trap
c.It cannot be connected to plastic pipe
d.Its configuration tends to self-siphon and lose the trap seal
Explanation
An S-trap discharges vertically in a way that tends to self-siphon, pulling out the water seal and allowing sewer gas into the building. Cost, pipe material, and cleanout size are not the reason; the prohibition exists because the trap seal cannot be reliably maintained.
Law Reference: 2025 CA Plumbing Code, Chapter 10 (Traps)Practice all 700 questions free — no signup required.
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