Sink backs up when the garbage disposal runs

Symptoms

• Water rises in the sink while the disposal runs
• Backup subsides once the disposal is turned off
• Gurgling accompanies the backup
• Problem may affect the other basin too on a double sink

Likely causes

• CommonClogged disposal discharge tube or the trap right after itFood particles from the disposal often collect right where it connects to the drain line.
• PossibleDishwasher connection knockout plug not removedOn a newer disposal, forgetting this step can restrict flow through that inlet.
• PossibleGrease coating narrowing the shared drain lineFat from food waste can build up right past the disposal's outlet.
• PossibleOverloading the disposal with too much waste at onceCan temporarily overwhelm the drain line's capacity.

What to do

1. Turn off the disposal and let the sink settle before continuing.
2. Run water without the disposal running to see if the sink drains normally on its own.
3. If normal drainage confirms the disposal connection is the issue, disconnect the disposal's discharge tube (after unplugging the unit) and check for clogs inside it.
4. Clear any food debris found and reconnect the discharge tube securely.
5. Check the trap just past the disposal connection for grease buildup and clean it if needed.
6. Run the disposal briefly with water on to test if the backup recurs.
7. Going forward, run cold water while the disposal is on and avoid grinding fibrous or starchy waste in large amounts.

Tools and parts

• Adjustable pliers
• Bucket

When to call a pro

Call a plumber or appliance tech if the disposal connection is clear but backup continues, since the clog may be further down the shared line.

Safety