A P-trap is a curved section of pipe found under most sinks. Its main job is to trap water in the bend, which helps block sewer gases from coming up into your kitchen or bathroom. This water barrier also catches small debris, making it easier to retrieve items that accidentally fall down the drain. P-traps are a standard part of plumbing and are required by most building codes for safety and hygiene reasons.

If you notice a bad smell coming from your sink, it could be due to a dry P-trap or a buildup of debris. When the water in the trap evaporates—often in sinks that aren't used often—sewer gases can escape. Sometimes, food particles or hair can get stuck and start to smell. Running water down the drain regularly and cleaning out the trap can help reduce odors. If the smell continues, checking for leaks or blockages may be helpful.

Signs of a clogged P-trap include slow draining water, gurgling sounds, or water backing up in the sink. You might also notice an unpleasant odor. To check, you can remove the P-trap (after placing a bucket underneath to catch water) and look for any trapped debris. If you're not comfortable doing this, a plumber can help inspect and clear the clog safely.

The "135 rule" in plumbing refers to the angle at which pipes should be installed to promote smooth water flow and reduce the risk of clogs. Instead of sharp 90-degree turns, using 45-degree or 135-degree fittings helps water and waste move more efficiently through the system. This is especially important when connecting P-traps to other drain pipes, as it can help prevent blockages and make maintenance easier.

To pick the right P-trap, check the diameter of your sink's drain pipe. Most bathroom sinks use a 1-1/4 inch P-trap, while kitchen sinks often need a 1-1/2 inch size. It's important to match the P-trap size to your existing plumbing for a proper fit and to prevent leaks. If you're unsure, bringing a photo or measurement to the store can help you find the right option for your setup.