How to Fix a Leaking Pipe Under Sink

How to Fix a Leaking Pipe Under the Sink

Finding a puddle under your sink is alarming — but in most cases, the fix is simple. Leaks under the sink are almost always caused by a loose connection, a worn slip joint washer, or a cracked P-trap. Here's how to find and fix it.

Step 1: Find the Source of the Leak

Dry everything under the sink with a towel, then run water and watch carefully. Common leak locations:

• Supply line connections — the braided lines connecting the shut-off valves to the faucet
• Shut-off valve — the valve itself may be leaking
• P-trap connections — the curved pipe under the drain
• Drain basket / strainer — where the drain meets the sink basin
• Garbage disposal connection — if you have one

Fix 1: Leaking Supply Line Connection

If the leak is at the threaded connection between the supply line and the faucet or shut-off valve:

1. Turn off the shut-off valve
2. Hand-tighten the connection first — sometimes it's just loose
3. If still leaking, disconnect the supply line, wrap the threads with PTFE thread seal tape, and reconnect
4. Tighten with a wrench — snug plus a quarter turn. Don't overtighten.

Fix 2: Leaking P-Trap

The P-trap is the curved pipe that holds water to block sewer gas. Leaks here are usually at the slip joint connections:

1. Place a bucket under the P-trap
2. Hand-loosen the slip nuts on both ends of the P-trap
3. Remove the P-trap and inspect the slip joint washers inside the nuts — replace them if flattened or cracked
4. Clean the P-trap while it's out
5. Reinstall with new washers and hand-tighten the slip nuts, then snug with pliers

If the P-trap itself is cracked, replace the entire section — they're inexpensive at any hardware store.

Fix 3: Leaking Drain Basket

If water leaks from where the drain meets the sink basin:

1. The plumber's putty or gasket under the drain basket has failed
2. Remove the drain basket from below (unscrew the locknut)
3. Clean off old putty, apply fresh plumber's putty around the drain flange
4. Reinstall and tighten

Emergency Temporary Fix

If you need to stop a pipe leak immediately while you get parts:

• Self-fusing silicone tape — wrap tightly around the leak point for a temporary waterproof seal
• Epoxy putty — knead and press over the leak for a fast temporary fix

Bottom Line

Most under-sink leaks are fixed by tightening a connection, replacing a slip joint washer, or resealing the drain basket — all simple repairs that take under 30 minutes. Find the exact source first, then apply the right fix.