How to Repair a Leaking Sink Drain

Drainage systems under the sink are designed to be watertight without being overtightened, but years of thermal expansion and contraction often cause these connections to vibrate loose. When you notice a steady drip, your first instinct might be to reach for a wrench, but the fix is usually much simpler and requires more finesse than raw power. Done well, a drain repair restores a dry cabinet floor and ensures your trap seal remains intact, preventing sewer gases from entering your home. You are essentially troubleshooting the path of least resistance for water; by cleaning the joints and ensuring the gaskets are seated perfectly, you eliminate the leak entirely without needing a plumber.

1. Clear the Cabinet Space. Empty the cabinet entirely of all cleaning supplies and stored items. Place a shallow basin or a large towel directly beneath the P-trap to catch residual water.
2. Pinpoint the Leak. Wipe all joints dry with a clean rag. Run the faucet and observe the joints while holding a dry tissue; the tissue will darken instantly if it touches even a minor leak.
3. Tighten the Slip Nuts. Try hand-tightening the plastic slip nuts on the trap assembly. If they are already snug, use tongue-and-groove pliers to turn them another quarter turn, but do not overtighten or the plastic will crack.
4. Swap Out the Washers. If tightening fails, unscrew the slip nuts and remove the P-trap. Inspect the beveled plastic or rubber washers; if they are deformed, cracked, or hardened, replace them with new ones.
5. Clean the Threaded Surfaces. Use an old toothbrush or a rag to scrub away any debris, soap scum, or old plumber's putty from the threaded pipe ends. A clean surface allows the new washer to create a perfect seal.
6. Reassemble and Verify. Realign the pipes, slide the washers onto the pipes, and tighten the slip nuts by hand until they meet resistance. Give them a final quarter-turn with pliers, then run the water to verify the leak is gone.