Install a P-Trap Under Your Sink

P-traps are the curved pipes beneath sinks that hold a slug of water to block sewer gases from entering your home. Every drain needs one, and they're designed to come apart without professional help. The trap catches rings and debris, prevents nasty smells, and meets code requirements in every jurisdiction. You'll replace or install one when changing a sink, fixing a leak, or retrieving something valuable that went down the drain. The beauty of P-trap work is that it's entirely visible and accessible. No cutting into walls, no mystery connections behind drywall. Modern slip-joint connections use compression fittings that seal with rubber washers and hand pressure. The hard part isn't the assembly—it's getting everything aligned so the pieces actually want to connect. That means measuring correctly, understanding the slight flexibility built into the system, and knowing which direction those beveled washers face.

  1. Measure and dry-fit the assembly. Place a bucket under the work area. Hold the trap arm against the wall stub-out and the trap itself below the sink tailpiece. Note where cuts are needed on the tailpiece or trap arm to achieve proper alignment. Most traps allow 2-3 inches of adjustment, but if your measurements are outside that range, you'll need to cut PVC or chrome tube with a hacksaw. Dry-fit all pieces without washers to confirm everything reaches.
  2. Install the tailpiece and slip joint washer. Slide the slip nut onto the tailpiece, threads facing down, then add the beveled washer with the thick side up against the nut. Insert the tailpiece into the sink drain opening from below. The tailpiece should extend 4-6 inches below the sink, giving you room to attach the trap. If it's too long, mark it and cut with a hacksaw, then deburr the edge with sandpaper.
  3. Attach the J-bend to the tailpiece. The J-bend is the curved bottom section of the trap. Slide its upper slip nut and washer onto the tailpiece, washer bevel facing up. Push the J-bend up until it seats firmly against the washer, then hand-tighten the slip nut. The trap should hang level and plumb. Don't wrench-tighten yet—you need adjustment room for the next connection.
  4. Connect the trap arm to the wall stub. The trap arm is the horizontal pipe that connects the J-bend to the wall. Slide the wall-end slip nut and washer onto the trap arm, then insert it into the wall stub-out pipe about an inch. The washer bevel faces away from the wall. Loosely thread the slip nut onto the stub's threads. Now adjust the trap arm's position in the J-bend opening—it should slide in about an inch—and loosely attach that connection with its slip nut and washer.
  5. Align and hand-tighten all connections. With all pieces loosely connected, adjust the entire assembly so nothing binds or twists. The J-bend should hang plumb, the trap arm should have a slight fall toward the wall, and all pipes should align without forcing. Once positioned correctly, hand-tighten each slip nut as firmly as possible. The rubber washers compress to create the seal, not the metal threads.
  6. Snug connections with slip-joint pliers. Use slip-joint pliers to give each nut an additional quarter-turn past hand-tight. Go gently—you're compressing rubber, not cranking metal. PVC threads strip easily if over-tightened. Work from top to bottom: tailpiece connection first, then J-bend to trap arm, finally trap arm to wall. Check that nothing shifted during tightening.
  7. Run water and check for leaks. Remove the bucket and run hot water at full pressure for two minutes. Watch every connection closely—leaks usually appear within seconds. Check by running your finger along each joint and looking for moisture. If you find a drip, try tightening that connection another eighth-turn. If it still leaks, disassemble, check the washer for damage or incorrect orientation, and reassemble.
  8. Fill the trap and verify the seal. Let the water run until the trap fills completely. The water seal prevents sewer gas from entering the room, so the trap should hold water even after you turn off the faucet. Open the cabinet and smell for any sewer odor—if present, you have a leak or loose connection. A properly installed P-trap holds its water seal indefinitely unless the drain goes unused for weeks.