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Sink drain plumbing · Repair Copilot

Leaky pipe under sink

A leak under the sink almost always comes from a loose slip-nut on the P-trap or a worn supply-line connection — parts you can reach and hand-tighten, no wall-opening required. Clear out the cabinet, point your camera at the drain, and a 30-year plumber persona helps you find exactly where it's weeping and stop it.

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Steps to fix leaky pipe under sink

  1. Empty the cabinet, put down a towel and a pan, and dry everything so you can spot exactly where fresh water appears.
  2. Run the tap and watch: a leak at the curved P-trap joints is a drain leak; a leak at the shutoff valve or braided line is a supply leak.
  3. For a drain leak, hand-tighten the plastic slip-nuts on the P-trap a quarter turn; if a nut is cross-threaded or a washer is flattened, take the trap apart and reseat it.
  4. For a supply leak, snug the compression nut at the shutoff or replace a cracked braided supply line — cheap and tool-light.
  5. Wipe it all dry, run water for a minute, and re-check each joint with a dry finger or paper towel.
  6. If it leaks from the wall behind the trap, from the main drain stack, or won't stop after reseating, call a licensed plumber before it rots the cabinet.

Safety first: if a step calls for gas, a main water or sewer line, a service panel or main breaker, or a sealed refrigerant system, stop and call a licensed pro — Repair Copilot will tell you when you're there.