What Is a P-Trap?
If you notice weird odors coming from your drain, you may have a P-trap problem
Highlights
P-traps are an essential part of your sink, shower, or bathtub drainage system.
The main function is to stop sewer gasses from wafting into your home.
P-traps also help prevent clogs by trapping debris.
They’re made up of three separate parts.
You can remove and reinstall your P-trap to fix leaks and clogs.
If you’ve ever looked beneath your bathroom sink, you’ve probably encountered a P-trap. This section of piping—which gets its name from its shape—is an essential part of the drainage systems found beneath your sink, shower, and bathtub. No bathroom is complete without it, even though we may roll our eyes at the storage space it takes up in our under-sink cabinets. So, what is a P-trap, and how does it work? This guide will tell you everything you need to know.
What Is a P-Trap?
Like other common plumbing terms, a P-trap is exactly what it looks like: a small section of curved piping that’s shaped like the letter P and found underneath sinks, bathtubs, and showers. As a crucial piece of your fixture’s drainage system, the P-trap has two main functions:
It prevents sewer gasses from escaping your drain line: The P-trap holds a continuous level of water that acts as an airtight seal and prevents sewer gasses from wafting up your drain into your bathroom. If you smell sewer gasses, it’s a good indication that your P-trap has either dried out or has a leak.
It prevents clogs: The curved shape of the piping traps debris like hair, sediment, and other solids, which prevents clogs deeper in your plumbing or municipal sewer system.
P-traps come in all different sizes for different fixtures. Most of the time, they’re made from PVC, but some are made from steel. The curved area holds about one and a half to two inches of water. When you use your plumbing fixture and water runs down your drain, it flushes out the old water in the P-trap and replaces it with new water.
Parts of a P-Trap
If you plan to install a sink drain, you’ll need to know the parts of a P-trap. Most P-traps are made from three separate pipes. Each part (as shown on the above P-trap diagram) has a different function:
Tailpiece: This vertical section of piping (also known as an inlet) attaches to the bottom of your drain and funnels wastewater into the J-bend, the curved section of your P-trap.
J-bend: This curved section of piping (also known as the trap) catches debris and holds a small amount of water that serves as a barrier against sewer gasses.
Wall tube: This section of piping (also known as an outlet) funnels water from the J-bend into the rest of your home’s drainage system.
Cleanout: The cleanout gives plumbers access to the P-trap so they can clear out smaller clogs and debris without removing pipes. The cleanout is typically located on the bottom of the J-bend curve, but some drainage systems have a separate cleanout pipe.
P-Trap vs. S-Trap
If you look under your sink and notice your P-trap has an extra curve, you don’t actually have a P-trap. Instead, you have an S-trap. Like the name suggests, this type of trap is shaped like the letter S. It was an old plumbing standard. In fact, it was the precursor to the P-trap that initially made flushable toilets a possibility.
S-traps no longer meet plumbing code. The design was phased out because the curves can siphon water out of the trap, eliminating the barrier and allowing sewer gas to seep into homes. If you have an older home that still has S-traps beneath your fixtures, you should hire a local plumbing repair service to replace them.
How to Remove a P-Trap
To fix a leaking P-trap, you’ll need to remove it. Before you start, place a bucket below the trap to catch water.
Gently loosen the nuts on either side of the J-bend pipe (you can use pliers if they’re particularly tough).
Note the placement of the washers so you can reassemble the P-trap later.
Once the trap is loose, pull it straight down to remove it.
Empty the water from the pipe into your bucket.
How to Reinstall a P-Trap
Reassembling your P-trap is fairly straightforward. Follow these steps:
Start by reinstalling the J-bend pipe on the wall tube.
Make sure to put the washer and nut back in place, but leave the connection loose.
Line up the J-bend pipe with the drain tailpiece.
Reinstall the J-bend pipe along with the washer and nut.
Check your work, then tighten the nuts to seal the connection.
Run the water to make sure there are no leaks.
If there are leaks, loosen the nut and check the placement of the washers. You may need to reinstall them.
Keep in mind, many clogs may be located deeper in your plumbing than the P-trap. In that case, it’s a good idea to hire a plumber.