What's that U-Shaped Pipe Underneath the Sink?

What's that U-Shaped Pipe Underneath the Sink?

It seems a bit counterintuitive. That pipe underneath the sink that curves upwards seems like it would prevent wastewater from moving into the sewer system with ease. In fact, you might find that many of the clogs that cause you trouble seem to originate within the bend of this pipe. So what’s its purpose, and how does it help your plumbing system?

Your bathroom doesn’t smell like sewage

And you’ve got that curvy pipe to thank. That piece of pipe is called the P-trap (because it looks like a sideways letter P), and it’s the reason you don’t smell the raw sewage moving down your drains. When you use your sink, a bit of water lingers around in the trap, and that serves as a shield that prevents smells from coming through.

In fact, all of your plumbing fixtures have a trap underneath, whether you can see it or not, for this very purpose. S-traps and J-traps are some other common shapes. The trap underneath your toilet bowl, for example, looks more like an S, and it’s often an internal trap built in to the fixture.

It’s a good thing that debris gets stuck in the P-trap

You might be frustrated by the fact that hair and other debris always seems to get stuck in this trap. But when you think about it, this is a very good thing. When debris is stuck in the sink trap, you can reach it with a very small drain auger. Without the trap, it would just move deeper in the drains, and you’d need an expert to use a very large drain auger at this point.

Besides, if you drop a ring in the sink, tub, or toilet, it’s a lot easier for a plumber to retrieve it when it’s only stuck in the trap!

Call Allstar Plumbing for drain cleaning and hydro jetting in Los Angeles, CA when your P-trap doesn’t do a good enough job of preventing major clogs.


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