How To Find The Source Of The Leak Under Your Sink

leak under sinkIf water gets loose under your kitchen sink, a leaky disposal is just one possibility. Under-sink leaks can be a multiple choice mystery with more than one likely suspect. Whatever the cause, they can rot the wall structure behind the cabinet, trigger mold growth and attract insects. They may also be the first sign of a more major event, like an impending supply line rupture that could cause water damage to a large area. From a leaky disposal to a loose drain fitting, here are some steps to rule out sources of kitchen sink leaks.

Disposal Leaks

  • Water may seep through a leaky disposal sink flange. Fill the sink with water, then run a piece of tissue around the disposal flange underneath the sink to detect drips or seepage.
  • Another possibility are drain lines connected to the disposal. The smaller dishwasher drain line attaches with a clamp that may be loose and leaking. The larger pipe goes down the household drain. It connects to the disposal with two screws that could be loose from vibration or a rubber gasket inside the connection may be defective.
  • If leakage originates from the internal seal at the bottom of the disposal body, this is an indicator that the unit must be replaced.

Leaky Supply Connections

Compression fittings at shutoff valves under the sink connect supply lines to hot and cold faucets. Because supply lines and connections are under household water pressure, leakage at these points may unexpectedly worsen and flood the kitchen.Wipe each connection with dry tissue. If moisture is detected, try to very gently tighten the compression fitting with a wrench. If that doesn’t work, the supply line and fitting may need replacement.

Drain Leaks

Fill the sink with water, then watch underneath as it drains. Look for leakage around the slip joints in the drain pipe. Hand-tightening the large joint nuts slightly may stop leakage. If that fails, drain pipes may need to be disassembled and new joint seals installed.


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