Quick Answer:
If the P-trap slips loose every few weeks it’s usually a worn or misinstalled slip-joint washer, cracked plastic slip nuts, or a misaligned tailpiece and trap arm. Start by checking washer orientation, replace any cracked plastic nuts, and verify pipe alignment before reassembling. Tighten hand-tight plus a small quarter turn with pliers — avoid overtightening.
Why This Happens
- Worn or reversed slip-joint washers lose their seal and allow movement at the joint.
- Plastic slip nuts can crack or deform over time, so the joint no longer stays snug.
- Misaligned pipes (tailpiece and trap arm) put side-load on the nut and cause it to loosen as the sink is used or bumped.
- Loose sink fixtures or vibrations from piping stress the trap connection. If you also see water after you use the sink, check for related symptoms like Bathroom sink leaks under cabinet.
Step-by-Step What to Do
Tools and materials to have ready
- Bucket or shallow pan
- Adjustable pliers or slip-joint pliers
- Replacement slip-joint washers (cone) and replacement slip nuts (plastic or brass)
- Soft cloth and small brush for cleaning
1. Prepare and catch water
- Place the bucket under the trap to catch water. You usually do not need to shut off house water for the trap itself.
- Loosen the slip nut by hand, then with pliers if needed; remove the trap carefully and empty into the bucket.
2. Check washer orientation and condition
- Remove the cone-shaped slip-joint washer and inspect for cracks, flattening or hardening.
- Install the washer so it seats properly: the tapered/cone side should seat into the tailpiece or the fitting where it forms the seal. Replace any damaged washers.
3. Replace plastic nuts if they’re damaged
- Inspect both slip nuts for hairline cracks, stripped threads, or deformation.
- Replace worn plastic nuts with new ones — or use brass slip nuts if you prefer more durable hardware. Make sure the new nut threads match the size of the trap and tailpiece.
4. Verify pipe alignment before tightening
- Reassemble the trap loosely and check that the tailpiece and trap arm are straight and seated without sideways tension.
- If pipes are misaligned, adjust the tailpiece length or use an adjustable trap arm so joints sit squarely. Support the tailpiece or trap arm if needed to prevent movement when tightening.
5. Tighten correctly
- Tighten the slip nuts by hand until snug, then give about a quarter turn with pliers. Over-tightening can crack plastic nuts or crush washers and cause future leaks.
- Run water and watch for leaks for several minutes, then re-check after a day of normal use to confirm the fix.
What Not to Do
- Do not glue slip-fit traps. Gluing prevents future service and can cause damage when you must remove the trap.
- Do not overtighten plastic slip nuts — they crack easily.
- Do not rely on chemical drain cleaners to fix mechanical leak or alignment problems; they won’t stop a loose joint and can damage components.
When to Call a Professional
- If the trap keeps loosening after you replace washers and nuts and correct alignment.
- If the tailpiece or trap arm is cracked, badly corroded, or the sink’s mounting hardware moves when you touch it.
- If you notice recurring leaks that have led to cabinet water damage or if related fixtures show symptoms like a persistently stiff handle such as faucet handle hard to turn.
Safety Notes
- Wear gloves to avoid contact with standing water and debris from the trap.
- Use a bucket to catch water and protect flooring and cabinet interiors.
- Avoid using excessive chemical cleaners while you work; they can splash and irritate skin or eyes. Rinse contaminated surfaces thoroughly if exposed.
Common Homeowner Questions
- Why does the trap still loosen after I tighten it?
A worn washer, cracked nut, or misalignment is still present — replace the washer/nut and realign the pipes. - Can I swap plastic nuts for metal ones?
Yes. Brass or chrome-plated nuts are more durable; ensure the thread size and fit match the trap and tailpiece. - Will screwing the nut on extra tight keep it from coming loose?
No. Overtightening can strip threads or crack nuts. Tighten by hand, then a small additional turn with pliers.