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Everything You Need to Know About P-Traps

Everything You Need to Know About P-Traps

Feature photo courtesy of @scenes_on_summercrest

Most people don’t spend much time thinking about the plumbing under their sinks, tubs, and showers. However, the curving pipe connecting the basin to the drain pipe — also called the P-trap or S-trap — is an essential part of the setup. Understanding how the P-trap works and how to replace one that’s worn out is useful knowledge for any homeowner.

What Exactly Is a P-Trap?

A P-trap is a pipe that runs under a sink, shower, or bathtub and serves a very important purpose in the kitchen or bathroom’s plumbing system. The curved design holds water to create an airtight seal in the pipe. This prevents bacteria, debris, and gases from backing up into the sink or tub. It also traps the occasional hair, food, or small object, such as an earring.

P-traps have been around for centuries, ever since people figured out they prevent clogs and make the room smell better. They come in multiple materials, including polypropylene, ABS, PVC, and brass.

  Photo courtesy of @merrillconstruction

P-Trap vs. S-Trap


Homes built in the early 20th century may have an S-trap under the sink. Named for its distinctive S-shaped curve, the S-trap serves the same purpose as the P-trap. However, the design also makes it more likely to siphon away too much water, leaving behind a dry trap. Without the water creating the seal, unwanted and potentially dangerous gases can enter the home.

The design of the P-trap is an improvement over the S-trap and helps keep water in the trap — and its seal in place. It is possible for a P-trap to go dry, but it’s much less likely than with an S-trap. Today, S-traps do not meet building codes, and although some are still in use in older homes, they are illegal in new constructions


How to Remove and Replace a P-Trap

Replacing a P-trap is an easy DIY job for a homeowner. In many cases, they can remove the parts by hand, but a pair of water pump pliers (also called V-jaw tongue-and-groove pliers) can come in handy if the nut holding the P-trap in place is hard to turn. Here’s how.

  1. Place an empty bucket under the P-trap. Keep some towels nearby to dry up any spills.
  2. Unscrew the nut holding the pipe in place. Use the pliers if necessary.
  3. Let the water inside the pipe drain into the bucket. Note the location of the washers on the pipes.
  4. Examine the inside of the pipe and remove visible clogs and debris. Avoid using harsh cleaners that can damage the pipe.
  5. Reassemble the P-trap, starting with the end that connects to the drain line. Make sure the washers are in the correct position.
  6. Position the other end of the pipe in place. This may require some careful maneuvering to line up the pieces.
  7. Tighten the nut around the pipe. It should be secure but not so tight that the pipe splits.

After replacing the P-trap, it’s time to check the connection and make sure it’s not leaking. Turn on the water and let it run for a few seconds, long enough to check the pipe itself for a leak. If the pipe fits securely, fill the sink with a couple of inches of water. Then unplug the sink, so all the water drains at once, and examine the pipe for signs of a leak. Filling the sink and releasing it adds extra pressure to the pipe and its fittings.

Decorating Tips for Showcasing a P-Trap

Homeowners who still have an S-trap under the sink should consider replacing it, but they don’t have to wait until there’s a plumbing problem to replace the pipes under the sink or tub. A P-trap is a functional piece that also adds to the décor of the room. It creates an interesting focal point in a room with a vintage or industrial design and under a wall-mounted sink. Try the following tips for showcasing a P-trap in the bathroom.

Photo courtesy of @charestvalentine

Show Off the P-trap

In many bathrooms, a cabinet hides the plumbing under the sink. Consider rem