Summary
This article explains what a P trap is, where it is found, and how it prevents sewer gases from entering a home. A short video at the top covers the basics and common questions.
When to use this
Use this guide if you are:
Curious about plumbing components under a sink
Noticing sewer or drain odors in a bathroom or kitchen
Maintaining plumbing in a vacant or infrequently used property
Learning basic plumbing concepts
Video: What Is a P Trap?
This video explains what a P trap is, how it works, and why it is an essential plumbing component.
Overview
A P trap is a curved section of pipe installed beneath plumbing fixtures such as sinks, tubs, and showers. Its primary purpose is to hold water that creates a seal between the living space and the sewer system.
This water seal helps protect indoor air quality and prevent odors.
Common Questions Covered in the Video
What Is a P Trap and Where Is It Found?
P traps are commonly found:
Under bathroom and kitchen sinks
Beneath tubs and showers
On other fixtures that connect to a drain line
They are typically shaped like the letter “P” when viewed from the side.
Primary Function of a P Trap
The P trap holds a small amount of water that blocks sewer gases from traveling back up through the drain and into the home.
Do All Fixtures Require a P Trap?
Most plumbing fixtures require a P trap. Toilets are an exception because they have an integral trap built into the fixture itself.
Integral Trap in a Toilet
A toilet’s internal design includes a built-in trap that performs the same function as a P trap, preventing sewer gases from entering the bathroom.
How the Water Seal Works
The water inside the P trap acts as a physical barrier. As long as water remains in the trap, sewer gases cannot pass through.
What Happens if a P Trap Is Dry?
If the water in the P trap evaporates or drains away, sewer gases can enter the home, often causing noticeable odors.
Keeping a P Trap Full in a Vacant House
The video discusses ways to ensure traps remain full of water in homes that are vacant or rarely used, helping maintain the seal.
Troubleshooting
Sewer odor near a drain → P trap may be dry
Fixture not used for long periods → Water may have evaporated
Visible leak under sink → P trap connections may be loose
FAQs
Q: How can I tell if a P trap is dry?
A: A dry P trap often results in sewer or drain odors coming from the fixture.
Q: Does running water fix a dry P trap?
A: Yes. Running water refills the trap and restores the seal.