What Is a P-Trap and Why Does It Dry Out?

The P-trap is a U-shaped section of pipe beneath your sink. Its job is simple: it traps a small amount of water after each use. That standing water acts as a seal, preventing sewer gases from drifting up through the drain and into your bathroom or kitchen.

Every time you run the faucet, old water flushes out and fresh water refills the trap. As long as the trap stays filled, the seal holds. If the water level drops, the seal breaks. Then you may notice a musty or rotten smell near the sink, which is a clear sign the trap has dried out.

The most obvious sign is a foul odor coming from the drain. The smell often resembles rotten eggs or sewage. You might also hear gurgling sounds from the drain when water runs elsewhere in the house, which can mean the trap seal is weak or missing.

Dry traps are not usually a water damage risk by themselves. The bigger concern is that sewer gases can enter your living space. If the smell persists after you refill the trap, the issue may be a cracked pipe or a venting problem, which needs a closer look.

The easiest way to keep a P-trap from drying out is to use the sink regularly. Running water for a few seconds every week refreshes the seal. If you leave home for a while, pour a little vegetable oil into the drain before you go; the oil floats on the water and slows evaporation.

Inspect under-sink pipes now and then for drips or loose connections. Tighten slip nuts gently by hand, not with a wrench, to avoid cracking the fittings. If you live in Doral, where heat and humidity can speed up evaporation, a monthly check of rarely used sinks is a smart habit.