What Is a P-Trap and Why Every Drain Needs One

A P-trap is one of the most common fixtures in household plumbing: the recognizable curved section of a drain line shaped like the letter “P” (or sometimes “S,” depending on the setup). Its job is simple but essential—it uses a water seal to stop sewer gases and odors from coming up through your drains.

Because many drains connect to the same sewer system, gases can travel back toward living spaces. Without a barrier, odors and potentially harmful gases could move through plumbing openings every time water flows or when pressure changes occur.