How to Fix a Leaking Sink Drain

Drips beneath your bathroom vanity are more than just a nuisance; they are a slow-motion threat to your cabinetry and floor joists. Moisture sitting in the dark, enclosed space of a vanity creates a perfect breeding ground for mold and can cause particleboard to swell and disintegrate long before you notice the structural damage. Fixing a drain is a tactile task, not a complex mechanical one, and the success of the repair depends on your ability to re-seat the seals properly. Done well, this project restores a bone-dry connection that stays tight for years. It requires you to be methodical about cleaning the pipe threads and ensuring the beveled edge of the rubber gasket points toward the joint. If you approach this with patience, you will save yourself a hefty plumbing bill and ensure that your bathroom remains protected from water damage.

  1. Clear Your Work Space. Empty the vanity completely and place a shallow basin or a folded towel directly beneath the P-trap. Removing the clutter ensures you have enough room to maneuver a wrench without knocking over cleaning supplies.
  2. Disconnect the Trap. Loosen the slip nuts on both ends of the P-trap using your hands or channel-lock pliers if they are seized. Slide the nuts down and remove the trap, allowing the standing water to drain into your basin.
  3. Check the Washers. Check the rubber washers or gaskets inside the slip nuts for cracks, flattening, or debris. If the rubber feels brittle or has lost its original shape, it must be replaced.
  4. Scour the Threads Clean. Wipe the threads of the tailpiece and the trap arm with a rag to remove grit, old pipe dope, or mineral buildup. A smooth surface is essential for the washer to achieve a watertight compression seal.
  5. Seat the New Washers. Slide the new slip nuts and tapered rubber gaskets onto the pipes in the correct orientation. Ensure the tapered (beveled) side of the gasket faces toward the fitting you are connecting to.
  6. Tighten and Verify. Hand-tighten the slip nuts firmly, then give them an additional quarter-turn with pliers to ensure a snug fit. Run the faucet for two minutes and dry the exterior of the pipe with a paper towel to check for any slow beads of water.