How to Replace Bathroom Sink Drain Slip Joint Washer

Step 1: Confirm the leak is really coming from a slip-joint washer

1. Dry the drain pipes, slip-joint nuts, and the cabinet floor with a towel.
2. Place a dry paper towel or rag under each drain connection you can reach.
3. Run the faucet for about 30 seconds, then stop the water and let the sink drain fully.
4. Watch for drips at the slip-joint nuts on the trap, trap arm, or tailpiece connection.
5. Check that the leak is not coming from the faucet supply lines, shutoff valves, sink strainer body, or a cracked pipe.

If it works: You have confirmed the drip starts at a slip-joint connection, which makes worn or misaligned washers the right repair to try first.

If it doesn’t: If the water is coming from the sink drain flange, a cracked trap, or the supply plumbing, fix that problem instead of replacing the slip joint washers.

Step 2: Set up the area and take the joint apart

1. Put a bucket or bowl under the trap to catch standing water.
2. Loosen the leaking slip-joint nut by hand. If needed, use pliers gently so you do not crush the nut.
3. Slide the nut back and separate the pipe pieces just enough to remove the old washer.
4. Pour the water from the trap into the bucket and wipe the pipe ends clean.
5. Keep the nut with the same connection so you can put it back in the same order.

Step 3: Match and install the new washer

1. Remove the old washer and compare its size and shape to the replacement.
2. Choose a new washer that matches the pipe diameter and fits the nut correctly.
3. Slide the slip-joint nut onto the pipe first if it came off, then install the new washer in the same orientation as the old one.
4. Seat the washer evenly so it is not twisted, folded, or cocked to one side.
5. Push the pipe pieces back together fully before threading the nut on by hand.

Step 4: Tighten the joint evenly

1. Hand-tighten the slip-joint nut until it feels snug and the pipes stay aligned.
2. If needed, give the nut a small additional turn with pliers. Use only enough force to compress the washer and stop the leak.
3. Check that the trap still lines up naturally and is not being forced sideways or upward.
4. Repeat the same washer replacement at any other slip-joint connection that was leaking or disturbed during the repair.

Step 5: Test the repair with a normal drain cycle

1. Dry every repaired joint completely so new drips are easy to spot.
2. Run warm water into the sink for a minute, then let the basin drain while you watch the repaired connections.
3. Fill the sink partway and release the stopper to send a stronger flow through the drain.
4. Wipe around each nut with a dry finger or paper towel to check for slow seepage.

If it doesn’t: If you see a small drip, tighten the leaking nut just a little more and test again. If it still leaks, reopen the joint and check the washer fit and orientation.

Step 6: Make sure the fix holds in real use

1. Empty the bucket, wipe the cabinet dry, and leave a dry towel or paper towel under the drain for the next day or two.
2. Use the sink normally several times, including a full-basin drain if that is when it used to leak.
3. Check under the sink after each use for fresh drips, dampness, or water marks around the repaired joints.

If it works: The area stays dry through normal use, confirming the new slip joint washers are sealing properly.

If it doesn’t: If dampness returns only during heavy draining, inspect the repaired joint again and replace any damaged nut or misaligned trap section that is preventing a good seal.