Follow the pipe from the bottom of the sink drain to its intersection with the P-shaped pipe, known as the P-trap, which prevents harmful fumes from rising to the surface of the sink. The P-trap joins the drainpipe to the P-trap arm.
Position a bucket beneath the P-trap. Loosen the slip-joint nut at each end of the P-trap by hand.
Disconnect the trap from the drainpipe and P-trap arm. Empty the water inside the P-trap into the bucket.
Loosen the slip-joint nut that connects the P-trap arm to the drain stub-out, which protrudes from the side of the wall. The P-trap arm joins the P-trap to the stub-out.
Disconnect the loosened P-trap arm from the stub-out.
Loosen the slip-joint nut from the top of the drainpipe and disconnect the loosened pipe from the drain.
Remove the old washers from inside each of the slip-joint nuts.
Fit a washer onto the head of the drainpipe. Position the washer so the flat side faces the slip-joint nut.
Join the drainpipe to the bottom of the drain. Tighten the slip-joint nut by hand.
Slide a washer, the flat side facing the slip-joint nut, onto both ends of the P-trap arm.
Attach the straight end of the P-trap arm to the stub-out. Tighten the slip-joint nut by hand.
Slip a washer onto the lower end of the drainpipe. Slide a second washer onto the jutting end of the P-trap arm. In both instances, position the washer to face the slip-joint nut.
Attach the P-trap at one end to the drainpipe. Attach the other end to the P-trap arm.
Tighten slip-joint nut at each end of the P-trap.