What is a P-trap?
A P-trap is the U-shaped bend in a drain pipe, usually located directly beneath a sink, that traps water to create a seal blocking sewer gas from entering the home.
The P-trap is the curved section of drain pipe that sits under your sink, toilet, or shower. It looks like an upside-down P (or a U shape) and holds standing water inside the bend. That water creates a seal that prevents sewer gases and odors from backing up through the drain line into your home.
Every fixture with a drain to the sewer system needs a P-trap for this reason. When you run water down a sink, it flows through the P-trap and carries waste out to the main line. The curve naturally retains a small amount of water even after the water drains out. If a P-trap dries out, loses its seal, or becomes blocked, you'll typically notice either sewer smells coming from the drain or slow drainage. A missing or damaged P-trap can also allow rodents and insects to enter through drain lines.
P-traps are usually made from PVC, metal, or chrome-plated brass. They're simple to replace if they crack or corrode, though a backed-up or clogged trap may require drain-sewer cleaning services to clear the blockage. Keeping the seal intact is one of the most basic lines of defense in home plumbing.