How to Replace a Leaking P-Trap Under a Kitchen Sink

P-traps fail. They corrode from the inside, crack under pressure, or the rubber washers wear out and stop sealing. When water pools under your sink, it's almost always the trap—the U-shaped section of pipe that holds standing water to block sewer gases from coming back up into your home. The good news: replacing one is a straightforward job that takes less than an hour and requires only basic tools. You don't need a plumber's ticket to do this right. What matters is understanding that the trap sits at the lowest point of the drain system, so water will come out when you open it. That's why every step starts with positioning a bucket. A leaking trap isn't something to leave alone. Water that drips into the cabinet below can soften the plywood base, rot the flooring underneath, and eventually damage the structure. More immediately, it smells. The standing water in a failed trap can't seal off the drain line properly, so you'll notice sewer odors rising up through the sink. Replace the trap, and both problems vanish. This is one of the few plumbing repairs where the parts cost less than the coffee you'll need to think about hiring someone else.

1. Stop Water Before You Start. Locate the shut-off valve under the sink—it's usually a small handle on the cold-water line coming from the wall. Turn it clockwise until it stops. If there's no valve, you'll need to shut off water at the main. Once the valve is closed, open the faucet above to relieve pressure. Place a bucket directly under the trap to catch standing water and any remaining liquid in the pipe.
2. Locate and Loosen Both Nuts. Look at the underside of the trap. You'll see two hexagonal nuts: one where the drain tailpiece (coming down from the sink) meets the top of the P-trap, and one where the trap connects to the drain line going into the wall. These are compression nuts. Using an adjustable wrench, grip the nut closest to the sink and turn it counterclockwise. You may need a second wrench to hold the fitting steady while you turn the nut. Do the same for the nut where the trap enters the wall.
3. Extract and Clear Connections. Once both nuts are loose, the trap will drop. Lower it into the bucket to catch any remaining water inside. Inspect the two threaded fittings where the trap connected—one on the tailpiece, one in the wall drain. Use a rag to wipe away debris, old washers, and corrosion from each fitting. Look inside each fitting opening; you should see the threaded surface clearly.
4. Replace Worn Seals and Rings. The compression nut works by squeezing a rubber washer (also called a seal) against a conical ferrule, which is a metal ring. When you remove the old trap, the washers and ferrules often stay inside the nut. Pull the old washer and ferrule out of each nut and discard them. Insert a new rubber washer into each nut, followed by the new ferrule. These come in the new trap kit, or you can buy them separately for a few dollars.
5. Connect Top Fitting First. Hold the new P-trap in place under the sink so the upper opening aligns with the tailpiece and the lower opening aligns with the wall drain. Start with the upper compression nut—the one going on the drain tailpiece. Thread the nut by hand (no wrench yet) until you feel resistance. The washer and ferrule should seat gradually as you tighten. Once hand-tight, use your adjustable wrench to turn it another quarter turn. Don't over-tighten; compression fittings fail when forced.
6. Secure Bottom Connection Gently. Now thread the lower compression nut (the one going into the wall drain) by hand until snug. Use the wrench to turn it a quarter turn more. Again, the goal is a snug seal, not maximum force. Step back and make sure the trap hangs naturally and isn't twisted. The curve should point downward in a smooth U-shape.
7. Watch for Leaks Under Pressure. Turn the shut-off valve counterclockwise to restore water pressure. Let the faucet run for 30 seconds to clear any air in the line. Watch the connection points on the trap. Place a dry paper towel under each nut. If water beads up on the towel, you have a leak. Small seeps sometimes stop within a minute as the washer settles, but steady drips mean you need to tighten further.
8. Adjust with Precision, Not Force. If either nut leaks, use the wrench to turn it an additional quarter turn while holding the fitting steady with a second wrench. Turn the water back on and retest. Repeat in quarter-turn increments until the leak stops. Most seals grip after one or two adjustments. If tightening doesn't stop the leak after 3-4 attempts, the washer may be damaged—shut off water, remove the nut, replace the washer and ferrule, and reinstall.
9. Inspect Every Connection. Run water at the sink for two minutes continuously. Look at the cabinet floor and all visible piping. Check the shut-off valve connection above the trap, the tailpiece coming down from the sink, and any additional drain lines that may be present. Shine a flashlight into dark corners. Water pooling anywhere—even a small puddle—means a fitting needs attention.
10. Verify Seal and Drainage. Fill the sink bowl halfway with water and let it drain completely. The trap should fill as the sink drains, and you should hear water gurgling through the system as it empties. This confirms the trap is holding its seal. You should also notice that any sewer smell that was present before is now gone—the standing water in the trap is blocking the drain line again.
11. Finish and Verify Everything. Empty the bucket and dry the cabinet floor. The old trap can go in the trash; it's not hazardous. If you removed the bucket before fully draining the old trap, wipe up any residual water. Check that you haven't left tools or debris under the sink. Close the cabinet door and test the sink one more time from above to confirm everything is working.