If the drain pipe under your sink is dripping, don’t ignore it. A leaking sink trap (also called a P-trap) can damage cabinets, flooring, and stored items. Fortunately, many sink trap leaks are caused by loose connections, worn washers, or inexpensive parts that are easy to repair or replace.
Quick Answer
Find the Leak
Common Causes of Sink Trap Leaks
How to Tighten a Leaking Trap
How to Replace a Sink Trap
Repair or Replace?
When to Call a Plumber
FAQs
Quick Answer
Most sink trap leaks are caused by loose slip-joint nuts, worn washers, cracked plastic fittings, corrosion, or misaligned drain pipes. Start by tightening the trap connections and inspecting the washers. If the trap is cracked, corroded, or continues leaking after repair attempts, replacing the entire trap assembly is usually inexpensive and straightforward.
Before replacing a trap, place a dry paper towel beneath each connection and run water through the sink. The wet spot often reveals the exact source of the leak and may save you from replacing parts unnecessarily. Of course be aware that a drip is likely to start at a fitting and travel down to the bottom of the trap.
Find the Leak
Before taking anything apart, identify exactly where the water is coming from.
Common leak locations include:
- Slip-joint nuts
- Trap washers
- The trap bend itself
- The trap arm connection
- The sink tailpiece connection
- Cracks in plastic fittings
- Corroded metal pipes
Dry the entire trap assembly thoroughly with a towel.
Then:
- Place a bucket beneath the trap.
- Run warm water through the sink.
- Watch each connection carefully.
- Use a flashlight if necessary.
- Identify the first location where water appears.
Sometimes water from a higher leak runs along the pipe and drips from a lower point, making diagnosis tricky.
Common Causes of Sink Trap Leaks
| Problem | Most Likely Cause | Typical Fix |
|---|---|---|
| Leak at slip-joint nut | Loose connection | Tighten nut |
| Leak after tightening | Worn washer | Replace washer |
| Leak from trap body | Crack or corrosion | Replace trap |
| Leak after recent repair | Misaligned pipes | Realign assembly |
| Slow drip from metal trap | Internal corrosion | Replace trap |
| Repeated leaks | Damaged fittings or threads | Replace assembly |
How to Tighten a Leaking Trap
Many leaks can be stopped without replacing any parts.
Step 1: Inspect the Slip-Joint Nuts
Look for the large threaded nuts that join the trap components together.
These are the most common leak points.
Step 2: Tighten the Connection
Plastic trap nuts should usually be tightened by hand.
If necessary, use slip-joint pliers to give the nut an additional quarter turn.
Do not overtighten.
Excessive force can crack plastic fittings or distort washers.
Step 3: Test for Leaks
Run water through the sink for several minutes.
If the leak stops, the repair is complete.
If the leak continues, disassembly and inspection are usually required.
How to Replace a Sink Trap
If tightening doesn’t solve the problem, replacing a trap is often the easiest solution.
PVC replacement traps are inexpensive, widely available, and resistant to corrosion.
Tools & Materials
- Bucket
- Slip-joint pliers
- Replacement P-trap kit
- Replacement slip washers
- Rags or towels
Step 1: Place a Bucket Under the Trap
The trap always contains water.
A bucket prevents spills inside the cabinet.
Step 2: Disconnect the Slip-Joint Nuts
Loosen the nuts connecting the trap to the tailpiece and trap arm.
Remove the trap carefully.
Step 3: Inspect the Components
Look for:
- Cracked plastic
- Corrosion
- Damaged threads
- Flattened or hardened washers
Step 4: Install the New Trap
Assemble the replacement trap according to the manufacturer’s instructions.
Ensure all washers face the correct direction.
The tapered side should generally point toward the fitting being sealed.
Step 5: Hand Tighten First
Tighten all slip-joint nuts by hand.
Then use pliers only if necessary.
Step 6: Test the Repair
Run water through the sink and inspect all connections carefully.
Tighten slightly if needed.
PVC traps are usually my recommendation for most homeowners. They’re inexpensive, easy to install, resistant to corrosion, and generally less troublesome than older chrome-plated metal traps.
Repair or Replace?
| Condition | Recommended Action |
|---|---|
| Loose slip-joint nut | Tighten connection |
| Worn washer | Replace washer |
| Minor misalignment | Realign trap |
| Cracked PVC trap | Replace trap |
| Corroded metal trap | Replace trap |
| Multiple recurring leaks | Replace complete assembly |
When to Call a Plumber
Contact a plumber if:
- The leak is coming from inside the wall.
- The drain pipe is severely corroded.
- The trap continues leaking after replacement.
- You suspect a larger drain or vent problem.
- The cabinet or floor has suffered water damage.
FAQs
Why does my sink trap leak only when the sink drains?
This usually indicates a problem with the trap connections, washers, or the trap itself rather than a supply-line leak.
Can I use plumber’s putty on a leaking trap?
No. Trap leaks should be repaired by tightening connections, replacing washers, or replacing damaged components.
How long does a sink trap last?
PVC traps often last decades. Metal traps may fail sooner due to corrosion.
Should trap nuts be hand-tightened?
Yes. Most plastic trap connections are designed to be hand-tightened, with only minor additional tightening if necessary.
Can I replace a P-trap myself?
Most homeowners can replace a standard sink trap using basic tools and an inexpensive replacement kit.
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