How to Repair a Leaking Sink Drain

Drips under the sink are a classic nuisance that can lead to cabinet rot if ignored for too long. A leaking drain isn't usually a sign that your plumbing is failing; it is almost always a result of a gasket that has hardened over time or a threaded connection that has worked itself loose during normal use. Fixing this is a straightforward mechanical process of disassembly, cleaning, and resealing. When done correctly, the connection will be watertight and require no further attention for years. Focus your effort on ensuring the surfaces are clean before applying any new sealant, as old debris is the most common cause of a repeat leak.

1. Empty and Protect the Cabinet. Empty everything from underneath the sink and place a bucket or deep pan directly beneath the drain pipes. This captures the water that will inevitably spill once the trap is broken.
2. Disconnect the P-Trap. Loosen the slip-joint nuts on either side of the P-trap by hand or with channel-lock pliers. Carefully lower the trap to drain the remaining water into your bucket.
3. Find the Failing Seals. Check the plastic or rubber washers found inside each connection point. If they are cracked, flattened, or brittle, they must be replaced.
4. Scrub Every Surface Clean. Use a stiff brush or a damp cloth to scrub away old putty, mineral buildup, and gunk from the pipe threads. A clean thread ensures a uniform, tight seal.
5. Seal the Flange Tight. If the leak is at the drain flange inside the sink, remove the old putty and roll a new rope of plumber's putty between your hands. Press it firmly into the drain opening before reinstalling the drain assembly.
6. Reassemble Without Overtightening. Reassemble the trap and pipes, tightening the nuts by hand first. Use pliers to give them an additional quarter-turn, but be careful not to overtighten, as this can crack plastic pipes.
7. Verify Every Joint Is Dry. Run a full basin of water and pull the stopper to let it drain rapidly. Watch each joint closely with a flashlight to verify there is no moisture weeping from the connections.