A kitchen sink cabinet is open revealing the P-trap.

What’s a P-Trap For Anyway?

Most plumbing pipes are hidden behind walls, above ceilings, or under floors -- the exception is that curved section of pipe beneath your kitchen and bathroom sinks. It’s called the P-trap, and it’s easily accessible for a reason: You can easily remove it to clear a clog or retrieve jewelry you accidentally dropped down the drain. But the P-trap plays a more important role than that: It prevents dangerous sewer gases from entering your home.

How a P-Trap Works

The P-trap takes its name from its shape -- it looks like an inverted P. The deep U section traps water, sealing out sewer gas and odors from leaking into your home. An outside vent -- a long, vertical pipe connected to the drain -- equalizes the pressure so that the P-trap always contains a plug of water.

Common P-Trap Problems

If you smell a foul odor coming from your drain, your P-trap may have lost its seal. Here’s how it can happen:

  • The P-trap dried out: If you haven’t used the sink in a while, the P-trap can dry out. This is a simple fix -- just run the tap for a few seconds to refill it.
  • The P-trap lost water through capillary action: Imagine dipping a tightly rolled sheet of paper towel into a cup of water. You’ll see the water soaking up through the towel. That’s called capillary action, and the same thing can happen in your drain. Strands of hair in the pipe can draw water out of the bend. In a sense, the liquid in the pipe climbs up the strands like a rope. As the water leaks out, sewer gases enter.
  • The P-trap empties due to a blocked vent stack: The vent stack is the vertical pipe sticking up out of your roof. It regulates air pressure throughout your home’s plumbing system. When the vent is blocked by debris, draining water can suck out the seal as air is pulled from the drain. A gurgling drain is a sign of a compromised vent.

Turn to the Phoenix Plumbing Repair Pros

At Plumbing & A/C Medic, our top priority is fixing your plumbing issues promptly and reliably. Whether it’s a clogged drain or something more major, no job is too big or too small for us. To schedule your appointment, call (602) 975-2306.