How to Find and Fix a Bathroom Sink Leak

Water is relentless, and a small drip beneath your bathroom sink can quickly escalate from a nuisance to a ruined vanity cabinet. The key to stopping a leak is patience; rushing in with a wrench often creates more problems than it solves by cracking aged plastic or stripping soft metal threads. Done well, this repair leaves your plumbing bone-dry and your cabinets protected from rot. You are looking for the point of entry—where the water beads—and addressing the seal, the nut, or the gasket responsible for failing. Work deliberately, keep a bucket handy, and focus on the connections where pipes meet one another or the sink basin.

1. Clear the cabinet first. Empty everything from underneath the sink. Lay down a dry towel or place a small bucket directly under the P-trap to catch any water that spills during the inspection.
2. Find the leak point. Wipe all pipes completely dry with a cloth. Run a dry paper towel along each joint and connection; the towel will instantly show a dark wet spot where a leak is hidden.
3. Tighten the slip nuts. If the leak is at a slip nut, use your hand or channel-lock pliers to tighten it clockwise. Do not overtighten, as plastic threads are fragile and easy to snap.
4. Swap the rubber washer. If tightening doesn't work, unscrew the leaking connection and remove the slip nut. Replace the old rubber gasket inside with a new one of the exact same diameter.
5. Clean and reseat the trap. Unscrew the two nuts holding the U-shaped P-trap in place. Clean out any hair or debris inside, inspect the rubber O-rings, and reseat the trap before tightening the nuts.
6. Run the final test. Turn the faucet on full blast for one minute. Check every joint you touched with a fresh, dry piece of toilet paper to confirm there is zero moisture.