Quick Answer:
If your kitchen sink gurgles when the dishwasher drains, it’s usually a venting or partial blockage issue where air is being pulled through traps or pushed back through the sink drain. Start with a few targeted checks on the dishwasher connection, garbage disposal, sink trap, and venting to find the cause. Don’t ignore it — the sound is an early sign of a developing drain problem.
Why This Happens
Gurgling happens when air and water compete for the same space in the drain lines. Common causes:
- Dishwasher drain hose or air gap is blocked or installed without a proper high loop or air gap, allowing dishwasher discharge to push air into the sink line.
- Partial blockage in the sink tailpiece, P-trap, or building drain that slows flow and traps air pockets.
- Faulty or missing venting (roof vent or air admittance valve) so air can’t move freely through the drain system.
- Problems at connected appliances — a garbage disposal with trapped food or a dishwasher check valve that fails to close.
Grease and food buildup often make these worse, and can also lead to odors — see Kitchen Sink Smells Like Grease After Cooking for cleaning tips related to buildup.
Step-by-Step What to Do
1. Observe and duplicate the sound
- Run the dishwasher while someone listens at the sink. Note whether gurgling happens only when the dishwasher drains or whenever sinks drain.
- Run the sink faucet while the dishwasher drains to see if the sound changes or if water backs up.
2. Check the dishwasher drain connection
- Inspect the drain hose route: it should have a high loop up to the underside of the countertop or an air gap to prevent backflow into the sink line.
- Look for kinks, clogs, or a collapsed hose. Disconnect and flush the hose if you suspect a clog (follow manufacturer guidance).
3. Inspect the garbage disposal and knockout plug
- If you have a disposal, run it with plenty of water to clear trapped food. Turn power off at the wall before reaching inside.
- Ensure the dishwasher hose is connected to the disposal on the correct inlet and that any knockout plug was removed when the disposal was installed.
4. Check the P-trap and tailpiece
- Put a bucket under the P-trap, loosen the slip nuts, and remove the trap to check for clogs or buildup. Clean and reinstall with proper seals.
- If the trap is clear but gurgling continues, the blockage may be deeper in the branch drain.
5. Test venting behavior
- Run water in multiple fixtures (sink plus a bathroom on the same floor). If you hear gurgling or air noises from other drains, the vent may be restricted.
- Check for an air admittance valve (AAV) under the sink. A failed AAV can cause gurgling; replace if old or sticky.
6. Targeted partial clearing
- Use a plunger on the sink after sealing the overflow to try to dislodge partial blockages. Use gentle, controlled strokes.
- If plunging fails, a small hand auger for sink drains can reach the P-trap and tailpiece. Don’t force an auger into the main line.
7. Final checks
- Run the dishwasher by itself and then with the sink faucet on to confirm the problem is fixed.
- Clean the sink aerator and check faucet flow; problems at the aerator can sometimes mislead you about sink drainage—see Kitchen Sink Sprays Sideways From Aerator for aerator checks.
What Not to Do
- Avoid forcing fittings or over-tightening plumbing joints; this can crack pipes or break fittings.
- Do not use caustic drain chemicals to clear clogs near appliances or disposals — they can damage seals, harm disposals, and are hazardous to handle.
- Don’t ignore early warning signs like gurgling or slow drainage; small problems can become full blockages or sewage backups.
When to Call a Professional
- Persistent gurgling after you’ve cleaned the trap and checked the dishwasher hose or disposal.
- Backups or sewage smell from multiple fixtures, which suggests a main drain or sewer issue.
- If you’re uncomfortable disconnecting plumbing, working near electrical disposals, or if vents are inaccessible on the roof.
Safety Notes
- Turn off power to the garbage disposal at the wall before working on it. Never put your hand into a disposal unless power is disconnected.
- Wear gloves and eye protection when removing traps or using mechanical tools. Have a bucket ready for water in the trap.
- Avoid chemical drain cleaners; they can cause burns and damage plumbing. Use mechanical methods first and call a pro if needed.
Common Homeowner Questions
- Why does only the sink gurgle when the dishwasher runs? It often means air is being forced back through the sink drain because of a high-resistance spot or missing/failed vent in that branch.
- Can I fix this without tools? You can try basic flushing, checking visible hoses, and running the disposal if you have one, but clearing deeper blockages usually needs simple tools or a pro.
- Will this damage my plumbing if ignored? Ongoing gurgling signals worsening blockage or vent problems and can lead to backups or odor issues, so it should be addressed promptly.