Small bucket or shallow pan
Use it for: Catches the water and debris that spill out when the trap is removed.
Shop small drain catch pansBathroom sink drain repair
How to Replace a Bathroom Sink P Trap Washer Set
If your bathroom sink is dripping from the slip-joint connections under the basin, replacing the bathroom sink p trap washer set is often the right fix.
This repair is usually straightforward: catch the water, remove the trap, replace the old washers, and reassemble the joints so the trap seals evenly. The key is using the right size washers and seating them in the correct direction.
Before you start: Match the pipe diameter, inlet and outlet configuration, and trap style before ordering.
Safety first
- Wear gloves if the trap water is dirty or has been sitting for a while.
- Keep a towel and bucket in place before loosening the trap so spilled water does not damage the cabinet.
- Use pliers gently on plastic nuts and pipes to avoid cracking them.
- Do not force misaligned drain parts together just to make the trap fit.
Tools you may need
Channel lock pliers
Use it for: Helps loosen and snug slip-joint nuts if they are too tight by hand.
Shop channel-lock pliers
Old towel or rags
Use it for: Protects the cabinet floor and wipes the pipes clean before reassembly.
Shop cleaning rags
Flashlight
Use it for: Lets you see the washer seats and check for hairline cracks or misalignment.
Shop flashlights
Soft brush or old toothbrush
Use it for: Cleans buildup from the trap and slip-joint sealing surfaces.
Shop cleaning brushesAs 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 leak is coming from the trap washers
- Run a small amount of water in the sink while watching the P-trap and both slip-joint nuts underneath.
- Dry the trap with a rag first so you can tell where fresh water appears.
- Look for drips forming at the nut connections where the curved trap meets the sink tailpiece or the wall drain arm.
- Check for obvious cracks in the trap body, stripped nuts, or corrosion that has eaten through the pipe.
If it works: You have confirmed the leak is coming from a slip-joint connection where the trap washers seal.
If it doesn’t: If the leak is coming from the faucet supply lines, shutoff valves, sink drain flange, or a cracked trap body, this washer replacement is not the main fix.
Stop if:
- The trap or drain arm is cracked, badly corroded, or broken.
- The cabinet shows hidden water damage, mold, or soft wood from a long-term leak.
- The leak is coming from inside the wall rather than the exposed trap joints.
Step 2: Set up the area and remove the old trap
- Clear out the cabinet so you have room to work.
- Place a towel under the trap and set a bucket or shallow pan directly below it.
- Loosen the slip-joint nuts by hand first, then use pliers only if needed.
- Lower the trap carefully and let the trapped water drain into the bucket.
- Slide the old nuts and washers off the pipe ends and keep them nearby so you can compare sizes.
If it works: The trap is removed and the old washers are off the pipe ends.
If it doesn’t: If a nut will not loosen, apply steady pressure with pliers and support the pipe so you do not twist the wall stub-out or crack the tailpiece.
Stop if:
- A pipe inside the wall moves loosely when you try to loosen the trap.
- The sink tailpiece is split, badly bent, or too damaged to seal with new washers.
Step 3: Clean and inspect the sealing surfaces
- Wipe the trap, tailpiece, and wall drain arm clean so the washer seats are easy to see.
- Use a soft brush to remove sludge, old residue, and mineral buildup from the slip-joint areas.
- Inspect the ends of the pipes for chips, deep grooves, out-of-round sections, or cracks.
- Compare the new washers to the old ones and make sure the diameter and shape match the trap connections.
If it works: The pipe ends are clean and you have confirmed the new washer set matches the trap.
If it doesn’t: If the new washers do not match the old size or the pipe diameter, pause and get the correct set before reassembling.
Stop if:
- The trap pieces are warped or damaged enough that a new washer will not seat evenly.
Step 4: Install the new washers on the trap connections
- Slide the slip-joint nuts onto the pipe ends first if they were removed.
- Place the new washers in the same connection points as the old ones.
- Seat each washer so the tapered side faces into the fitting it will seal against and the flat side faces the nut in a typical slip-joint setup.
- Lift the trap back into position between the sink tailpiece and the wall drain arm.
- Thread the nuts on by hand and make sure the trap lines up naturally without being forced sideways.
If it works: The new washers are installed and the trap is assembled squarely by hand.
If it doesn’t: If the trap will not line up without strain, loosen the joints and reposition the pieces so the washers can seat evenly.
Stop if:
- The trap only fits when pipes are forced out of alignment, which can cause repeat leaks or cracked parts.
Step 5: Tighten the joints and check for immediate leaks
- Hand-tighten both slip-joint nuts until they feel snug.
- Use pliers to give each nut a small additional turn only if needed; do not overtighten.
- Wipe the joints dry so any new drip is easy to spot.
- Run water slowly for 15 to 30 seconds while watching both trap connections closely.
If it works: The joints stay dry during a slow-flow test.
If it doesn’t: If a joint drips, stop the water, loosen that connection, reseat the washer, confirm the taper direction, and retighten evenly.
Stop if:
- A nut will not tighten because the threads are stripped.
- The leak gets worse as the nut is tightened, which usually points to a cracked part, wrong washer, or cross-threaded connection.
Step 6: Test the repair under normal sink use
- Fill the basin partway and then let it drain all at once to put a full flow through the trap.
- Run the faucet for another minute and check the trap, nuts, and cabinet floor with a dry hand or paper towel.
- Look again after 10 to 15 minutes to make sure there is no slow seep at either joint.
- Put the cabinet items back only after the area stays dry.
If it works: The trap stays dry during a full drain and normal sink use, confirming the repair held.
If it doesn’t: If you still see moisture, recheck washer orientation, pipe alignment, and nut tightness. If the joints are assembled correctly and still leak, replace the damaged trap parts instead of the washers alone.
Stop if:
- Water is still appearing from a different part of the drain assembly or from inside the wall.
Replacement Parts
Find a bathroom sink p trap washer set on Amazon
Match the pipe diameter, inlet and outlet configuration, and trap style 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
- Both slip-joint connections stay dry during a slow-flow test.
- The sink drains normally without drips under the basin.
- A full basin drain does not produce seepage at the trap nuts.
- The cabinet floor remains dry after the sink has been used again later in the day.
FAQ
Do I need to replace the whole trap or just the washer set?
If the leak is only at the slip-joint connections and the trap body is not cracked or corroded, the washer set is often enough. If the trap itself is damaged, replace the trap assembly too.
Which way does a P-trap washer face?
On a typical slip-joint connection, the tapered side faces into the fitting and the flat side faces the nut. The washer needs to wedge evenly into the joint as the nut tightens.
Should I use plumber's putty or tape on P-trap washers?
Usually no. Slip-joint washers are meant to seal by compression. Adding tape or putty at those washer joints can interfere with proper seating.
Why is it still leaking after I installed new washers?
The most common causes are the wrong washer size, backward washer orientation, dirty sealing surfaces, cross-threaded nuts, or a trap that is being forced out of alignment.
Can I reuse the old slip-joint nuts?
Yes, if the threads are clean and not cracked or stripped. If a nut is damaged or will not tighten smoothly, replace it.