Why Are Both Sides of My Kitchen Sink Draining Slowly?

Start by checking whether other drains in the house are slow. If only the kitchen is slow, it is a kitchen branch problem you can usually clear yourself.

Graphic: summary of this guide, made by our team from the cited sources.

What each symptom points to

What you see	Most likely cause	Where to work
Both bowls slow, rest of house fine	Grease or food buildup in the shared trap or wall pipe	Trap first, then the pipe in the wall
Water rises in one bowl when the other drains	Clog downstream of the tee	Shared trap or wall pipe
Disposal side worse, other side slightly slow	Clog in or just below the disposal	Disposal outlet and trap
Dishwasher leaves water in the sink	Shared kitchen drain is restricted	Same as above
Kitchen, tub and toilets all slow or gurgling	Main drain or sewer line	Call a plumber

Step 1: Plunge correctly

Use a flat cup plunger, not a toilet plunger. Korky's instructions for sinks are to plug the second drain on a double-basin sink with a wet rag or stopper, cover any dishwasher air gap with a wet rag, and make sure there is enough water to cover the plunger cup (Korky). Then plunge steadily for about 10 to 15 seconds and check the drain; repeat a few times if needed.

If one side has a garbage disposal, InSinkErator says to turn the disposal on first and look for a whirlpool in the water. A whirlpool means the disposal is running and the drain line is clogged. To plunge, block the other sink opening, fill the sink with about four inches of water, and plunge over the disposal opening (InSinkErator).

Step 2: Clean the shared trap

If plunging doesn't help, the trap is the next stop. Put a bucket under it, unscrew the two slip nuts by hand or with pliers, and pull the U-shaped trap out. Rinse it in another sink or outside. While it's off, look into the pipe going into the wall with a flashlight. Building codes require a water seal of 2 to 4 inches in each trap (ICC IPC Chapter 10), so a trap full of grease has very little room left for water to pass.

Put the trap back with the washers facing the right way, hand-tighten the nuts and run water to check for drips.

Step 3: Clear the pipe in the wall

If the trap was clean, the clog is in the pipe going into the wall. With the trap off, feed a small hand auger (drain snake) into that pipe and turn it as you push. When you feel resistance, keep turning to break through or hook the clog, then pull it back. Reattach the trap and run hot water for a few minutes. Our guide to why a drain keeps clogging covers what to do when the same line clogs again and again.

About drain cleaners: Poison Control says many contain concentrated acids or alkalis that can cause serious burns, and pouring them into a sink full of standing water raises the risk of splash-back (Poison Control). If you have already poured one in, don't plunge or open the trap; tell the plumber what you used.

How to keep it from coming back

Seattle Public Utilities lists the foods that cause the most trouble: bacon grease and meat drippings, butter and cooking oils, gravy and sauces, dairy, and oils that harden when cool such as olive and coconut oil (Seattle Public Utilities). Let grease cool, wipe pans with a paper towel before washing, and use sink strainers.

For the disposal, InSinkErator recommends running it with a moderate flow of cold water and continuing for a few seconds after grinding, and never pouring grease or fat into it (InSinkErator).

When to call a plumber

Call if the auger won't get through, if other drains in the house are slow or gurgling, or if water backs up into the sink when the washing machine or dishwasher drains. That last one usually means a clog further down a shared drain line; see why a washing machine drains into the kitchen sink.