How to Fix or Replace a Leaky Sink Trap

Step-by-step advice on how to stop a drip from the drainpipe under your sink. Includes easy fixes or complete replacement.

Is the U-shaped drain pipe beneath your sink leaking? If that pipe, called a “trap” or “P-trap,” is leaking, either fix it or replace it with an inexpensive new one before water damages the area under the sink.

Look for where the drip is originating. In many cases, drips come from loose fittings, especially the coupling nuts that connect the pipe sections together (see illustration below). You can often stop a drip by simply tightening the coupling nuts. A helpful tool for this is a large pair of slip-joint pliers (also referred to as “tongue-and-groove pliers” or by the trade name Channellock® pliers).

How to tighten the coupling nuts

1. Open the jaws of the pliers wide enough to grip the coupling nut.
2. Tighten the nut by gently turning it clockwise until it’s snug. Apply strong pressure but don’t strip the threads by over-tightening. On a metal trap, tighten the coupling nuts hand tight plus about a half turn, using slip-joint pliers to grip the nut. On a plastic trap, just hand tighten, and, if needed, give the nut about a quarter of a turn with slip-joint pliers.

How to clean out the sink trap

If that doesn’t stop the leak, you may need to clean-out or replace the leaky sink trap.

1. Place a bucket beneath the trap.
2. Using slip-joint pliers, disconnect the coupling nuts that hold the trap to the tailpiece and drainpipe, turning them counterclockwise.
3. Be ready for water to briefly pour out of the disconnected pipe.
4. Once you have taken the trap apart, clean it out with a straightened wire coat hanger or take it outside and rinse it out with a garden hose.
5. Replace any corroded parts.
6. When reassembling it, first tighten the coupling nuts by hand and then tighten them with the slip-joint pliers, but don’t over-tighten.
7. Run the water and look for leaks. If you spot leaks, tighten the nuts a little more. If everything appears to be sound, place a newspaper under the sink and check the paper for signs of any dripping the next day.

To replace parts or the entire the sink trap

If that doesn’t work, loosen the coupling nuts and remove the entire trap.

1. 1. Check the large rubber slip washers or cone-shaped plastic washers that provide the watertight seal at each joint between the trap’s pipes. Rubber washers may leak as the rubber hardens over time. If they’re hard or deteriorated, replace them. Plastic-pipe traps are more likely to leak when the pipes or washers become misaligned, so check for alignment.
   2. Check the pipes for rust or corrosion. If s pipe is corroded or cracked, take it with you to the hardware store to buy an appropriate replacement. Replace the entire trap.

You can choose between chrome metal and PVC traps. PVC traps are inexpensive, durable, easy to work with, and don’t corrode the way chromed brass drainpipes do.