Quick answers

  • Shared drain: Your dishwasher and sink use the same drain pipe. A clog in that pipe causes backups when both run at once.
  • New garbage disposal? There is a plug inside the dishwasher inlet that must be removed at install. If it was missed, water has nowhere to go.
  • Grease buildup: The most common cause in older Winston-Salem and Kernersville homes is grease. Grease coats the pipe walls over decades until the drain can not keep up.
  • Easy first check: Run your garbage disposal before starting the dishwasher. This alone often stops the backup.
  • Still backing up? The clog is deeper in the drain line. Time to call a plumber.

When your sink fills up every time the dishwasher runs, it feels like two problems at once. It is really just one. Your dishwasher and sink share the same drain, most likely. When that drain gets slow, running both at once is too much and water backs up into the sink.

The cause is almost always one of three things. Two of them you can check yourself right now.

Why they share a drain

In most homes, dishwashers are right next to the sink. The dishwasher drains through a hose that connects to the garbage disposal or the sink pipe under the cabinet. Both then share one drain line to the main pipe. This works fine until something slows that shared line down.

The three most common causes

1. Grease and food buildup. This is the most common cause we see in Winston-Salem and Kernersville homes. Grease sticks to the inside of pipes. Food builds on top of it. Over time the pipe gets narrow and can not drain fast enough for both the sink and dishwasher at once. A drain snake can clear food but professional cleaning is needed for grease.

2. A full or slow garbage disposal. If the disposal is packed with food waste, the dishwasher has nowhere to drain. Run the disposal and let it clear fully before you start the dishwasher. This is the easiest fix and worth trying first. We will have more on disposal problems in our upcoming garbage disposal guide.

3. A missed knockout plug. Did the backup start right after a new disposal was put in? Disposals come with a small plastic plug inside the dishwasher drain inlet. It has to be knocked out during install. If the plumber or installer missed it, the dishwasher drain is fully blocked. This is a quick fix once you know what it is.

What to try first

Run the disposal until it is clear. Then start the dishwasher and watch the sink. If the backup stops, the disposal was the problem. If water still comes up, pour a kettle of hot water down the sink drain to loosen grease and try again. If that does not work, the clog is too far down to fix without a snake or other professional cleaning.

What about chemical drain cleaners? See our guide to Chemical Drain Cleaners for help deciding what to use. And NEVER use a drain cleaner in a garbage disposal!

When to call a plumber

Call a plumber if the backup happens every time no matter what or if other drains in the house are slow too.

We serve Winston-Salem, Kernersville, Greensboro, and the surrounding area. Call us and we will get you on the schedule fast. 336-203-2348