Quick Answer:
If your toilet makes a gurgling sound when the dishwasher drains, it often means the two fixtures share a drain or the venting is not working well. Run the dishwasher drain and observe the toilet; repeatable bubbling confirms shared drain effects. Stop the dishwasher if you see bubbling that could lead to a backup and follow the checks below.
Why This Happens
Dishwashers dump a lot of water quickly into your sink drain. If the sink, dishwasher and toilet share the same drain line or the vent is partially blocked, the rushing water can push air back through the toilet trap. That air shows up as gurgling or bubbling in the toilet bowl. A partial clog, a missing high loop or air gap on the dishwasher hose, or a blocked vent stack can all cause this.
For similar symptoms in different situations, see Toilet bubbles during storms and Toilet gurgles after replacing trap.
Step-by-Step What to Do
Step 1: Confirm the behavior
- Run the dishwasher drain cycle while someone watches the toilet.
- Repeat the test once or twice. Repeatable bubbling when the dishwasher drains is a strong sign the fixtures share the same drain or venting is poor.
- If you see rapid bubbling or any signs of sewage coming up, stop the dishwasher immediately.
Step 2: Check the dishwasher drain hookup
- Under the sink, make sure the dishwasher drain hose has a high loop (attached up near the underside of the countertop) or an air gap where required by code. This prevents backflow into the dishwasher.
- If the dishwasher drains into a garbage disposal, ensure the disposal knockout was removed and the connection is tight and clear.
Step 3: Clear simple blockages
- Run the garbage disposal (if present) to clear food waste that might be restricting flow.
- Use a sink plunger on the kitchen sink to try to dislodge partial clogs in the trap or drain line. Do not use chemical drain cleaners if you plan to have a plumber work on the drain.
- If the sink drain is still slow, a small hand-held drain snake for the sink trap can help clear hair and grease near the P-trap.
Step 4: Test again
- After clearing and confirming the high loop or air gap, run a short dishwasher cycle and observe the toilet. If bubbling is reduced or gone, the steps helped.
Step 5: Monitor and decide
- If bubbling continues, especially across multiple runs or with multiple fixtures, you likely have a larger clog or venting issue that requires professional attention.
What Not to Do
- Don’t keep running the dishwasher if it causes bubbling—address the drain; a plumber is appropriate.
- Don’t pour strong chemical drain cleaners into drains connected to the dishwasher. They can damage parts and create a hazardous mix if other products are present.
- Don’t disconnect electrical parts or work on the dishwasher plumbing without shutting off power and water, or without experience.
When to Call a Professional
- If bubbling keeps happening after you try the basic checks and clearing steps.
- If multiple fixtures back up, or you see sewage, strong odors, or overflow risks.
- If you suspect a blocked vent stack on the roof, or if you’re uncomfortable performing the checks above. These situations are best handled by a licensed plumber.
Safety Notes
- Stop the dishwasher and turn off the water supply if you see any sewage or overflowing water.
- Turn off power to the dishwasher at the breaker before working under the sink or near electrical connections.
- Avoid mixing cleaning chemicals and never use a chemical drain cleaner if you expect a plumber to work on the line.
Common Homeowner Questions
- Why does the toilet gurgle only when the dishwasher runs? — The dishwasher is forcing air and water into a shared drain; the air escapes through the toilet trap if venting or flow is restricted.
- Will a slow sink drain cause this? — Yes. A partial clog in the sink or shared drain makes the dishwasher discharge more likely to push air and cause toilet bubbling.
- Can I fix this myself? — You can try the basic checks: confirm the issue, ensure a high loop/air gap, run the disposal, and clear the P-trap. If bubbling persists, call a plumber.