How to Repair a Leaking Under-Sink Pipe

Pipes under the bathroom sink are often out of sight until the moment you notice a damp cabinet floor or a persistent drip. Most of these leaks originate at the threaded slip joints where the pipes connect, usually because the rubber washer has dried out or the connection has vibrated loose over time. Repairing this is a classic weekend win that requires little more than a pair of pliers and a bucket. When done well, you will have a watertight seal that lasts for years without the need for pipe tape or messy sealants. Keep your cool, work slowly, and avoid overtightening, which is the fastest way to crack the plastic fittings found in most modern bathroom vanities.

1. Clear the Cabinet Fast. Empty everything out of the cabinet under the sink to give yourself clear access. Slide a bucket or plastic basin directly under the P-trap to catch any residual water once you break the seal.
2. Test Before You Disassemble. Try tightening the plastic slip joint nuts by hand. If they are loose, turning them clockwise might stop the leak immediately without further disassembly.
3. Break the Seal Safely. If tightening fails, unscrew the slip nuts by hand. Pull the P-trap section of the pipe away from the drain tailpiece and the wall pipe, allowing the water in the trap to drain into your bucket.
4. Find the Real Culprit. Check the rubber slip joint washers inside the nuts for cracks, brittleness, or debris. Clean the threads on the pipes to ensure no buildup prevents a tight seal.
5. Seat It Straight, Tighten Smart. Slide the new washers and nuts onto the pipe ends in the correct order. Push the pipe sections together and thread the nuts back onto the housing, tightening them firmly by hand.
6. Verify the Seal Holds. Turn on the bathroom faucet and let the water run for a full minute while watching the joints. Use a dry paper towel to wipe around each connection to see if any moisture clings to the surface.