How Much Does It Cost to Fix a Trap Leak Under a Bathroom Sink?

What you're actually paying to fix

A trap leak that only shows downstairs is almost always a small problem hiding behind a scary symptom. The trap part costs $12 to $15. The stress comes from where the water ends up.

That's the whole job.

Bring in a licensed plumber and it's $140–$320, mostly because of their minimum service call. The repair itself is fast; you're paying for the truck showing up.

The wild card is the ceiling below. Water that's been dripping for weeks can turn a $50 fix into a $500 drywall and paint job on top.

2026 cost breakdown

That's a trap kit, a washer pack, and maybe a new pair of channel-locks if you don't own them.

A licensed plumber runs $140–$320 for a standard trap repair. Most of that is the minimum service charge, which sits around $150 to $250 in most US metros in 2026, plus 30 to 60 minutes of labor and parts.

If the leak is at the wall stub-out and they have to reseat or replace the fitting, add $75 to $150.

Ceiling repair below is separate. A small drywall patch and repaint runs $150 to $500 depending on size, texture matching, and whether there's mold behind it.

So worst case, a neglected trap leak that soaked a finished ceiling can total $600 to $900 all in. Best case, you spend $50 on a Saturday morning.

• Professional repair typically runs $140–$320. This is not a DIY job, so plan on hiring a pro.
• Plumber, trap repair: $140–$320
• Wall connection repair add-on: $75 to $150
• Ceiling drywall patch and paint below: $150 to $500
• Mold remediation if present: $500 and up

How we built these numbers

The cost ranges come from typical 2026 US pricing: hardware-store trap kits and washer packs for the DIY figure, and standard plumber service-call minimums plus labor and parts for the pro figure.

The DIY range assumes you already own basic tools. If you need to buy channel-locks, you're at the top of the range.

The pro range reflects a straightforward trap repair with normal access. Wall work, ceiling repair, and mold are called out separately because they vary too much to fold into one number.

We rate this symptom DIY-friendly with high urgency: the fix is easy, but the water damage clock is ticking on whatever's below the leak.

What's leaking and why it shows up below

in most cases it's a slip-joint washer. The P-trap connects with hand-tightened nuts and beveled washers, and those loosen or harden over years.

Here's the part that throws people off: the water doesn't drip where it leaks. It clings to the pipe, runs to the lowest point, and drips off there. That lowest point can be inside the wall.

So you see a wet ceiling five feet from the sink and assume the whole system is failing. Usually it's one washer you can reach with your hand.

The next suspect is a cracked trap body. Thin chrome traps corrode from the inside out, and cheap PVC cracks if someone overtightened it. The crack often hides on the underside where you'd never look.

Then there's the wall connection. Where the trap arm slips into the drain stub-out in the wall, there's another washer and nut. When that fails, water runs straight down inside the wall and pops out on the ceiling below with zero warning at the sink.

How to find the real leak point

Don't guess. Dry everything and use paper towels to pinpoint the source.

Wipe down the entire trap, tailpiece, and wall connection until they're bone dry. Tear off strips of paper towel and drape one under each joint.

Run the water for 30 seconds, then check which towel got wet first. That joint is your leak. Ignore wherever the water eventually drips off; that's downstream noise.

Once you know the joint, try the cheap fix first: hand-tighten the slip nut a quarter turn and re-test with fresh towels.

If it still weeps, take that section apart. Look at the washer (hard, cracked, or misshapen means replace) and the nut flange (any crack means replace the nut).

For a full trap swap, buy a matching kit. Bathroom sinks are almost always 1-1/4 inch. Kitchens are 1-1/2 inch, so double-check before you buy.

• Channel-lock pliers (or just strong hands for plastic nuts)
• A bucket and rags for the standing trap water
• A 1-1/4 inch PVC trap kit, around $12 to $15
• A spare pack of slip-joint washers, around $4
• A flashlight or headlamp for the dark corner under the vanity

DIY or call a plumber

This is one of the safest plumbing jobs to do yourself. There's no pressurized water, no soldering, and the parts are cheap. If you can reach the trap and turn a nut, you can do this.

Do it yourself when the leak is at a visible slip joint, the trap body, or the tailpiece under an accessible vanity.

Call a pro when the leak is inside the wall, the metal nuts are corroded solid, the drain stub-out is loose in the wall, or you've replaced the trap twice and it still leaks (that points to damaged pipe threads or a bad drain body).

Also call a pro if opening the ceiling below reveals the leak is coming from something other than the trap, like a supply line or a different fixture's drain.

Can this wait?

A trap leak isn't a burst pipe. The trap only holds water and only sees flow when the sink drains, so nothing is spraying under pressure.

But it's still rated high urgency for a reason: the water is landing on a ceiling. Every day it drips, the drywall, insulation, and framing above soak up more.

A leak you catch this week might mean a paint touch-up. The same leak ignored for a month can mean cutting out ceiling, drying a cavity, and treating mold.

If you can't fix it today, at minimum stop using that sink and put a bucket or towel below the drip point. Then handle it within a few days.

How your home's age changes the job

In homes built before the 1980s, you'll often find chrome or brass traps with corroded nuts. Those can seize, and forcing them cracks the fitting. Budget for replacing the whole assembly, not just a washer.

Older homes also sometimes have S-traps or non-standard drum traps that don't meet current code. A plumber may recommend swapping to a proper P-trap while they're in there.

Homes from the 1990s onward usually have PVC traps that come apart easily. The failure mode there is a cracked body or an overtightened nut, both cheap fixes.

If your downstairs bathroom sits above a finished basement or a first-floor ceiling, the leak has farther to travel and more to ruin. That's the setup where waiting hurts most.