How to Fix a Leaking Pipe Under the Bathroom Sink

Water underneath your bathroom sink is a common nuisance that demands immediate attention before it warps your vanity cabinet or encourages mold growth. The culprit is almost always a loose connection or a degraded washer at the P-trap or tailpiece, which are the visible plumbing segments beneath the basin. Successfully sealing a sink drain is about patience and precision rather than brute strength. When done well, the joints will be snug, dry, and free of drips, ensuring that your vanity stays protected and your bathroom remains functional. Do not overtighten, as you can easily crack plastic pipes or deform rubber seals, which only leads to more leaking.

1. Clear your workspace first. Remove all cleaning supplies and vanity storage to provide a clear view of the piping. Place a bucket or a shallow tray directly beneath the P-trap to catch residual water.
2. Find the exact source. Dry the pipes completely with a rag and run the faucet while observing the joints. Identify the exact connection that is weeping water; look for beads of moisture forming on the underside of the nuts.
3. Loosen without stripping. Use your hands or a pair of channel-lock pliers to gently loosen the plastic slip nuts on the leaking section. If the nuts are metal and seized, apply a light penetrating oil and let it sit for ten minutes before turning.
4. Check the rubber washers. Remove the pipe segments and examine the rubber slip-joint washers for cracks, flat spots, or hardened debris. If they look worn or brittle, they must be replaced.
5. Reassemble with fresh seals. Wipe the threads on the pipes clean of any mineral buildup or old pipe dope. Slide the new washer onto the pipe, reinsert the pipe into the fitting, and thread the slip nut back on by hand.
6. Test the seal thoroughly. Tighten the nut by hand until it is snug, then give it a final quarter-turn with pliers. Turn on the water and observe the joint for several minutes to ensure the leak is resolved.