P-Trap Leaking Under Sink: How to Fix It
Water drips or pools under the sink, usually noticed when you open the cabinet doors, especially after running the faucet or draining a full sink.
DIY Cost
$5–$25
Typical Pro Cost
$150–$275
Tools Needed
- Bucket or shallow pan
- Channel-lock pliers
- Towels
- Flashlight
Parts Needed
- Replacement slip-nut washers
- Replacement P-trap assembly (if the pipe itself is cracked)
⚠️ Safety Warnings
- Don't overtighten slip nuts with pliers — plastic P-trap fittings crack under too much torque, turning a small leak into a bigger repair.
- Standing water under a sink near outlets or extension cords is a shock hazard — dry the area and check for nearby electrical before working.
Step-by-Step Instructions
Clear out the cabinet and place a bucket
Remove everything from under the sink and put a bucket or shallow pan directly under the P-trap (the U-shaped pipe) to catch water and debris during the fix.
Find exactly where it's leaking
Dry everything off with a towel, then run water and watch closely. Leaks almost always show up at one of the slip-nut connections (the ribbed plastic/metal collars where pipe sections join) rather than from a crack in the pipe itself.
Tighten the slip nuts by hand first
Try hand-tightening the slip nut at the leaking joint a quarter turn. Loose connections are the most common cause and often need nothing more than this.
Disassemble and inspect the washer if it still leaks
If hand-tightening doesn't stop it, use channel-lock pliers to loosen the slip nut, slide it back, and check the washer inside. A cracked, flattened, or missing washer is the next most common culprit.
Replace the washer and reassemble
Install a new washer (bring the old one to the store to match size/shape), make sure the pipe ends are pushed together fully and square, then hand-tighten the slip nut followed by a quarter turn with pliers — snug, not forceful.
Run water and check for drips
Run the faucet for a couple minutes and check every joint, then let a full sink drain at once (the higher flow rate reveals leaks a slow trickle won't).
When to Call a Professional
If the pipe itself (not a joint) is cracked, if the leak is coming from where the trap connects to the wall drain, or if tightening/rewashering the joints doesn't stop it, call a plumber — a damaged wall drain fitting isn't a DIY-friendly repair.