How to Fix a Leaking P-Trap Under the Sink

P-traps serve a vital purpose in your home by creating a water seal that prevents sewer gases from entering your living space. When you notice a drip or a damp cabinet floor, it is almost always due to a compromised seal at one of the threaded joints or a hairline crack in the plastic pipe itself. A properly functioning trap should be bone-dry and free of any white crusty mineral deposits. Successfully resolving this leak is a matter of methodical disassembly and inspection. You do not need to be a plumber to restore a watertight seal; you simply need the patience to ensure that every washer is seated perfectly before tightening. Done well, this repair will last for years without a single drop hitting your cabinet floor.

Protect Your Floor First. Remove all cleaning supplies and items from under the sink. Place a shallow bucket or a plastic basin directly beneath the P-trap to catch the residual water trapped in the bend.
Break the Bond Gently. Use your hand or large channel-lock pliers to unscrew the plastic slip nuts on both ends of the P-trap. Expect a small amount of water to pour out once the seal breaks.
Find the Culprit. Remove the slip nuts and the old conical washers from the pipe ends. Check the washers for cracks, hardening, or deformation and examine the pipe threads for any debris or physical damage.
Wipe Clean for Success. Wipe the pipe threads and the interior of the joints with a damp cloth to remove any soap scum or mineral buildup. Ensure the surfaces are smooth so the new washers can seat correctly.
Rebuild the Trap. Slide the new slip nuts and tapered washers onto the pipes, ensuring the tapered side of the washer faces the joint. Reconnect the P-trap to the drain tailpiece and the wall pipe, pushing them firmly together.
Verify the Seal Works. Tighten the slip nuts by hand until they are snug, then give them a final quarter-turn with pliers. Run water through the sink while watching the joints to ensure everything is perfectly dry.