One common reason for a smelly P-trap is that it's dry. The water in the pipe's bend creates a barrier that blocks sewer ...

Dry P-Trap. The P-trap may also be dry, meaning there is an issue inside the ventilation line. Plumbing vents pull air into the plumbing system to help move waste and wastewater through the pipes ...

Question: I hope you can help me resolve this problem. For about six months a very offensive odor has come in from my bathtub's drain. It seems to occur mostly in the evenings, but not every evening.

With an “S” trap drain, the trap is easily siphoned dry with each use and the water seal no longer exists. A properly installed “P” trap will always maintain a water seal.

Dry or dirty P-trap. A P-trap, or drain trap, is a U-shaped section of pipe that holds a small amount of water at all times to help prevent sewer gases from coming up through your drain.