Bucket or shallow pan
Use it for: Catches water left in the trap when you loosen the drain connections.
Shop bucket for drain workBathroom sink drain repair
How to Replace Bathroom Sink Slip Joint Washer
If your bathroom sink is dripping from a slip-joint connection on the drain trap, replacing the slip joint washers is usually the right fix.
These washers seal the hand-tightened drain connections under the sink. When they dry out, crack, flatten, or get installed backward, water can leak from the trap or tailpiece. This is a simple repair if the pipes are still in good shape.
Before you start: Match the replacement part to your exact bathroom sink before ordering.
Safety first
- Keep the work area dry so you do not slip while reaching under the sink.
- Use pliers gently on plastic nuts to avoid cracking them.
- Wear gloves if the trap water is dirty or the cabinet has sharp edges.
Tools you may need
Channel lock pliers
Use it for: Helps loosen stuck slip nuts without forcing them too hard.
Shop channel-lock pliers
Old towel or rags
Use it for: Wipes up water and lets you dry the joints so you can spot fresh leaks.
Shop absorbent shop towels
Flashlight
Use it for: Makes it easier to inspect the washers, nuts, and pipe ends under the sink.
Shop LED flashlight
Nylon brush or old toothbrush
Use it for: Cleans grime from the pipe ends and slip nut threads before reassembly.
Shop small cleaning brushAs an Amazon Associate I earn from qualifying purchases. Repair Riot may earn a commission at no extra cost to you.
Step-by-step fix
Step 1: Confirm the slip joint washer is the likely problem
- Dry the drain pipes, trap, and slip nuts under the sink with a towel.
- Run a small amount of water, then a fuller stream, while watching each slip-joint connection.
- Look for drips forming at the nut where two drain pieces slide together, such as the trap-to-tailpiece joint or trap arm joint.
- Check whether the nut is already snug by hand. A loose nut can mimic a bad washer.
- If the leak is coming from the sink drain flange, a cracked pipe, or the shutoff valves, this is not the right repair.
If it works: You have confirmed the leak is coming from a slip-joint connection on the sink drain.
If it doesn’t: If the water is coming from a different spot, diagnose that leak first before replacing the washers.
Stop if:
- The drain pipe is cracked, badly corroded, or split.
- The sink drain assembly itself is loose or leaking from above the slip-joint connection.
- The cabinet or wall shows hidden water damage, rot, or mold that needs a larger repair.
Step 2: Set up the area and take the joint apart
- Place a bucket or shallow pan under the trap.
- Remove items from the cabinet so you can work without bumping the pipes.
- Loosen the leaking slip nut by hand. If it is stuck, use pliers gently and turn only enough to free it.
- Slide the nut back and pull the joint apart carefully. Expect some water from the trap.
- If you are replacing more than one washer, take apart one connection at a time so the pipe layout stays easy to follow.
If it works: The leaking slip-joint connection is apart and the old washer is exposed.
If it doesn’t: If the nut will not loosen, apply steady pressure with pliers and support the pipe with your other hand so you do not twist the whole drain assembly.
Stop if:
- A plastic nut starts cracking or crumbling as you loosen it.
- A metal pipe or nut is seized so badly that forcing it may break the drain assembly.
Step 3: Remove the old washer and inspect the parts
- Pull out the old slip joint washer from the pipe or nut.
- Check the washer for flattening, cracks, hardening, or distortion.
- Wipe the pipe ends, the inside of the nut, and the sealing surfaces clean.
- Use a nylon brush or old toothbrush to remove grime from the threads and pipe edge.
- Inspect the pipe end where the washer seats. It should be smooth enough to seal and not chipped or badly out of round.
If it works: The old washer is removed and the joint surfaces are clean and ready for the new washer.
If it doesn’t: If the washer area is still dirty, clean it again so the new washer can seat evenly.
Stop if:
- The pipe end is broken, badly warped, or too damaged for a new washer to seal.
- The slip nut threads are stripped or cracked.
Step 4: Install the new slip joint washer the right way
- Slide the slip nut onto the pipe if it came off during disassembly.
- Place the new washer onto the pipe in the same position as the old one, with the tapered side facing into the fitting on most standard slip-joint connections.
- Push the pipe back into the fitting so the washer seats evenly.
- Slide the nut forward and thread it on by hand to avoid cross-threading.
- Hand-tighten the nut until snug, then give it only a small additional turn if needed. Do not overtighten plastic parts.
If it works: The new washer is seated and the slip nut is tightened evenly without forcing it.
If it doesn’t: If the nut will not thread smoothly by hand, back it off and realign the pipe and washer before trying again.
Stop if:
- The washer does not fit the pipe and nut correctly.
- The joint will only line up if the pipes are forced sideways, which can cause another leak.
Step 5: Reassemble the rest of the trap and check alignment
- If you opened more than one connection, replace the remaining washers the same way and reassemble each joint.
- Make sure the trap pieces line up naturally without strain.
- Hand-snug all slip nuts so the trap is supported evenly.
- Wipe every joint dry so you can spot any fresh water during testing.
If it works: The drain assembly is back together, aligned, and dry for leak testing.
If it doesn’t: If the trap looks twisted or under tension, loosen the nuts slightly, realign the pieces, and retighten by hand.
Stop if:
- The drain assembly cannot be aligned without bending or forcing the pipes.
- A connection keeps slipping apart because the wrong size washer or nut is installed.
Step 6: Test the repair under real use
- Run a slow stream of water for about 30 seconds while watching the repaired joint.
- Then fill the sink partway and let it drain to send a larger volume of water through the trap.
- Wipe a dry finger or paper towel around each slip-joint nut to check for moisture.
- If you see a slight drip, tighten the leaking nut a little more and test again.
- Check again after a few minutes to make sure no slow seep is forming.
If it works: The repaired slip-joint connection stays dry during both light flow and a full drain test.
If it doesn’t: If the joint still leaks after careful retightening, reopen it and check for a backward washer, debris on the seat, poor alignment, or the wrong washer size.
Stop if:
- The leak continues after reinstalling the washer correctly and confirming alignment.
- Water is now appearing from a different part of the drain assembly, suggesting another failed seal or damaged pipe.
Replacement Parts
Find bathroom sink slip joint washer on Amazon
Match the replacement part to your exact bathroom sink before ordering.
As an Amazon Associate I earn from qualifying purchases. Repair Riot may earn a commission at no extra cost to you.
Verify the repair
- The repaired slip-joint connection stays dry during a slow-flow test.
- The sink drains a fuller basin of water without drips at the trap or tailpiece joints.
- The trap sits in line without obvious twisting or side pressure.
- A recheck a few minutes later shows no slow seep around the slip nuts.
FAQ
Do I need to shut off the water to replace slip joint washers?
Usually no. You are working on the sink drain, not the supply lines. Just avoid running the faucet while the trap is apart, and keep a bucket underneath for the water left in the trap.
Which way does a slip joint washer face?
On most bathroom sink drain connections, the tapered side faces into the fitting and the flat side faces the nut. If you copied the old washer position before removal, install the new one the same way unless the old one was clearly backward.
Can I reuse the old washer if it looks okay?
It is better to replace it. Old washers often flatten or harden enough that they will leak again once disturbed.
Why is it still leaking after I replaced the washer?
The most common causes are a backward washer, dirt on the sealing surface, a misaligned trap, overtightening that distorts the washer, or the wrong size replacement. A cracked nut or damaged pipe end can also keep the joint from sealing.
Should I use plumber's putty or pipe dope on a slip joint washer?
Usually no. Slip-joint connections are meant to seal with the washer and proper alignment. Adding sealant can make diagnosis messier and usually does not fix a damaged or misfit joint.