USA Expert Plumbing

Kitchen sink backing up into the other sink

By USA Expert Plumbing Editorial Team. Updated . 1 min read.

Short answer

When water from one side of a double kitchen sink comes up the other, the clog is below the point where both sides join, usually in the shared trap or the branch drain in the wall. Plug one side and plunge the other, check the disposal, clean the trap, and snake the branch line if needed.

In this guide
  1. Where the clog usually is
  2. How to clear it
  3. When to call a plumber
  4. Prevent it
  5. Dishwasher and disposal connections

Both halves of a double sink drain into one pipe. If that shared pipe clogs, water from one side takes the easiest path, which is up and out the other side.

Where the clog usually is

  • The shared P-trap under the sink
  • The branch drain inside the wall, where grease builds up
  • The garbage disposal outlet or the dishwasher connection

How to clear it

  1. Check the disposal. Run it with cold water. If it hums without turning, turn it off at the switch and use the hex key on the bottom to free it.
  2. Plunge. Seal the other drain with a stopper or wet cloth, and plunge the clogged side firmly.
  3. Clean the trap. Put a bucket underneath, loosen the slip nuts, remove the trap and clear it. See our guide on how to clean a sink P-trap.
  4. Snake the branch line. With the trap off, feed a hand snake into the wall pipe.
  5. Reassemble and flush with hot water.

Never put your hand into a garbage disposal. Turn it off at the switch or breaker before working on it.

When to call a plumber

  • The clog is deep in the wall or main line
  • Other drains are also slow
  • Water backs up when the dishwasher runs even after clearing the trap

Prevent it

Keep grease and oil out of the sink, scrape plates into the trash, and run plenty of water with the disposal. See our drain cleaning cost guide for professional prices.

Dishwasher and disposal connections

The dishwasher usually drains through a hose into the disposal or a tailpiece. Many installations use a high loop or an air gap so dirty sink water cannot flow back into the dishwasher. When a new disposal is installed, the knockout plug inside its dishwasher inlet must be removed, or the dishwasher will not drain.

Common questions

Why does my dishwasher drain into the other sink?

The shared drain or disposal outlet is clogged, so the dishwasher water backs up into the sink.

Can I use a chemical drain cleaner on a double sink?

It often fails on grease clogs and makes later repairs hazardous. Mechanical methods work better.

Was this article helpful?

More in Emergency plumbing