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Sweetwater Plumbing Blog

The U-Shaped Pipe in Your Drains and What It Does

If you’ve ever looked under a sink or other plumbing fixture in a house, you’ll have noticed that the drain pipe has an unusual bend to it, a “U” shape, beneath the drain. If you’ve ever wondered what that peculiar bend in the drain is for, we have the answers for you here.

The U-Shape Is the P-Trap

If you tilt your head when you look at the bent pipe, you’ll see that it makes a “P” shape. This is where it gets its name: the P-trap. It’s a simple but ingenious piece of plumbing engineering that is designed to prevent sewer gas from coming back up the drain pipe and into your home.

When water runs down the drain, a small amount becomes trapped in the P-shape of this fitting. This water creates an airtight seal within the drain that blocks any foul smells from coming up the pipe the wrong direction. It’s effective, and most of the time you won’t even have to think about it.

The Dried-Out P-Trap

If a fixture receives regular use, the water in the P-trap will remain in place, sealing off the pipe. But if a fixture isn’t used for a few weeks, the water in the p-trap will eventually evaporate and leave the trap dry. When that happens, foul sewer odors will escape and you’ll start noticing awful smells in a part of the house.

Fortunately, it’s easy to solve this. Whenever you detect these bad smells, run water down the unused sink for about a minute. This will restore the water in the p-trap and fix the problem. Every week or so, make sure to run the water in any fixture that isn’t receiving regular use so the P-trap has its liquid seal.

If running water down the drain doesn’t stop the odors, you may have a more serious problem in the sewer line or drainage system. That’s when it’s time to call for professional plumbers.

Sweetwater Plumbing offers 24-hour emergency plumbing repair service in Ontario and throughout Southern California.

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