P-Trap
A U-shaped pipe under a fixture that blocks sewer gas from entering the home.
Definition
A P-trap is a curved section of drain pipe beneath sinks, tubs, and other fixtures that retains a water seal preventing sewer gases from venting back into living spaces.
In plain English
Every plumbing fixture must have a trap. A dry trap (from disuse) is the most common cause of mysterious sewer smells.
Example
A guest bathroom sink unused for months smells of sewer — running water for 30 seconds refills the P-trap and fixes it.
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