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What Is A P-Trap? Your Guide To Plumbing That Doesn’t Stink

No matter what type of home you live in, your plumbing should be up to code. You’ll need to ensure this whether you live in an apartment, house, modular home, or RV. One essential part of each drainpipe is a P-trap, or pee trap. Although it might have a funny name, its function is critical to preventing harmful gasses from entering your home. In addition, guests may think you’re unhygienic if your house smells like rotten eggs. Let’s learn more about P-trap plumbing and why it’s so crucial!

How Do P-Traps Work? 5 Drain Issues to Watch Out For

What Is a P-Trap?

A P-trap is a U-shaped bend in your plumbing drain that acts like a barrier. Because of the bend, a pocket of water sits there and prevents smelly odors from traveling through the plumbing into your house. It’s also helpful if you happen to drop something down the sink. The pee trap will block it from continuing down the pipe. You can usually retrieve the item at the P-trap.

If you look underneath your sink, you’ll probably see a pipe that has a dip. This is the bend in the P-trap that creates the water seal. They’re easy to access, easy to fix or replace, and easy to clean.

Why Is It Called A P-Trap?

The trap is called a P-Trap because of its shape. If you turn it sideways it forms the shape of the letter P. Some might call it a U trap or just the plumbing trap as its the most common type. There are however other types of plumbing traps so using the correct term will help prevent confusion.

P-trap
The P-trap provides a barrier to your plumbing against odors.

Do You Need a Pee Trap?

Yes, it’s necessary. In fact, the law requires you to install a P-trap wherever an open drain line expels wastewater into a drain-waste-vent system. Sewer gasses can be dangerous, so it’s crucial to have a pee trap in your plumbing lines at the sinks, showers, and bathtubs in your house. Plus, no one wants to smell that stink.

One place where we have experienced missing P traps is in European RV’s models. Instead of using P traps all the drains have plugs you are supposed to install when not using it. We can tell you firsthand that if you don’t have these drain plugs installed, particularly when starting to drive, the sewer gasses flood into the RV and make it smell terrible! P traps are required on American RV’s and work just like in a home. We have never experienced this issue in any of our RV’s.

Pro Tip: Doing your own plumbing? Find out Can You Connect ABS to PVC Pipe before you try your hand at repairing your pipes.

missing P Trap in RV plumbing
No P Trap Here. But they do have a cleanout. We can sure tell you it stinks!

What’s the Difference Between An S-Trap and a P-Trap?

An S-trap and P-trap have the same function. They prevent smelly gasses from entering your home by retaining water in the drain pipe. The only difference is the shape. A P-trap has a U-shape, while an S-trap looks like an S on its side. Since clogs are always a problem with these pipes, P-traps are more often in modern plumbing because of the fewer bends.

Pro Tip: Always have safe drinking water on the road by following these 7 Easy Steps to Clean and Sanitize Your RV Water Tank.

Pee trap installed under sink
Replacing and installing a P-trap is easy to do yourself.

Can I Install a Trap Myself?

Installing or replacing a P-trap under your sink can be a DIY project. You don’t have to call a plumber unless you don’t want to do the job. If you need to install a trap underneath your house to add plumbing for your bathtub, then you might want to call a professional.

When you look under the sink, you’ll see where the current piping goes through an opening in the wall. The trap arm is the shorter end and will usually go through this opening to connect to the rest of your drain pipe. The taller end of the pee trap will line up with the pipe coming out of your sink.

If you have a garbage disposal, the long arm of the trap will connect to it. The force of the water flowing through the pipe will move any debris or food chunks through the U-shape and down the drain pipe.

How Do I Know If My P-Trap Isn’t Working Properly?

P traps can quit working in two ways, first, they can clog and prevent the passage of water and second they can fail to prevent sewer gasses from getting past them.

If the P trap is not stopping gasses, the most common sign is the smell from the drain. A rotten egg smell signifies that hydrogen sulfide is in your home. P traps can quit stopping gasses if they leak or dry out. While it takes a very long time for a trap to dry out it can happen in dry climates. If the water in the trap has dried all that is needed is to run some more water in the sink.

Another tell-tale sign of a clog is when your drain doesn’t clear after you use it. You might also hear gurgling as water goes down the shower or bathtub drain. These signs indicate that you probably have a clog, and you’ll need to clean it as soon as possible.

Pee trap plumbing system
You’ll know your P-trap plumbing isn’t working correctly if you start to notice strong odors.

How Do I Clean Out the P-Trap Plumbing?

To prevent blockages, you should clean out your traps periodically. All you need for the task is a bucket and a pair of adjustable pliers. Place the bucket underneath the trap to catch water and debris in the pipe. Then loosen the nuts at the ends of the trap and remove the it slowly. You can empty the contents of the pee trap into the bucket. Once you remove it, you can clean it out. You can also clean out the adjoining pipes.

This is another reason people prefer a P-trap over an S-trap. With the extra bend in the plumbing, it can be more cumbersome to clean out an S-trap.

Pro Tip: Check out these Innovative RV Kitchen Sink Upgrades That Will Save & Purify Water.

How To Install P-Trap And Bathroom Sink Drain Piping | Easy Installation For Beginners!

Avoid the Stink: Make Sure Your P-Trap Is Working

P-traps are a necessary part of your plumbing system. They may be PVC pipe or steel, but no matter what the material, their function is essential. No one wants harmful gasses entering their house. Also, if you drop your precious wedding ring down the drain, you have hope that you can retrieve it!

When was the last time you cleaned out your traps? Tell us in the comments!

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About Tom Morton

Tom, a Pacific Northwest native, is our technical genius. Born in Washington and raised in Alaska before settling in Michigan. He's the man who keeps our operation running, both figuratively and literally.

With a background in Electrical Engineering, Tom specializes in RV solar systems and lithium batteries. He made history as the first documented individual to use a Tesla battery module as an RV battery. Tom has personally assisted countless RVers with system installations and has educated thousands more through his videos and articles.

Cinematography is another of Tom's passions, showcased in his work on the Go North series. You can see his camera skills on display in The RVers TV show on Discovery Channel and PBS where he also stars as a co-host.

Tom's mechanical expertise extends beyond RVs to boats, planes, and all things mechanical. He's renowned for taking on maintenance and repair projects single-handedly and is often spotted underneath RVs, making him the technical backbone of our endeavors.

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