Quick Answer:
Gurgling at the sink only when the dishwasher drains usually means air is being pulled through the trap or water is backing up due to a partial clog. Listen for air gulping and check whether the sink drains slowly even without the dishwasher—these are the main clues that tell you whether it’s a venting problem (air) or a clog (slow drainage).
Why This Happens
When the dishwasher pushes a surge of water into your sink drain or garbage disposal it displaces air and water farther down the line. If the drain line or vent is partially blocked, air must move through the trap to equalize pressure. That movement causes loud gurgles and can pull water out of the trap. A partial clog produces similar sounds because the water can’t flow freely and the system alternates between pressure and suction. Hearing an air gulping sound is a strong hint of venting or trapped air; slow draining without the dishwasher points to a clog.
Step-by-Step What to Do
1. Reproduce and listen
Run the dishwasher on a drain or rinse cycle with the sink empty and quiet. Stand close and listen for an air gulping sound. Note whether the gurgle happens only when the dishwasher drains or at other times too.
2. Check basic drain speed
Fill the sink with a few inches of water, then release it and time how fast it drains. Repeat with the dishwasher off. If the sink drains slowly even without dishwasher activity, you likely have a clog. If it drains fine except when the dishwasher runs, the vent or air path is the more likely cause.
3. Inspect the garbage disposal and hose connections
- Turn off power to the disposal before inspecting.
- Look at the dishwasher drain hose where it connects to the disposal or sink tailpiece. Make sure the hose is not kinked and the connection is tight.
- Run the disposal briefly (with power on) after clearing any visible debris to ensure the outlet is open.
4. Check the air gap (if present)
Many kitchens have an air gap on the countertop. Remove its cap and check for food or grit blocking the path. Clean it gently if needed; this can restore proper venting for the dishwasher.
5. Clear or inspect the P-trap
Place a bucket under the P-trap, loosen the slip nuts and inspect for clogs. Remove gunk and reassemble. If you’re not comfortable doing this, stop and call a professional.
6. Try a simple live test
Run hot water down the sink while the dishwasher is draining (open the faucet slightly). If the gurgling stops or improves, that suggests a venting issue; if nothing changes and water pools, a clog is likely. For related symptoms, you may also see Backup only when dishwasher finishes or the opposite behavior like a Sink fills with suds from dishwasher, which point to drain path problems.
7. When a DIY fix doesn’t help
If clearing the trap, checking the hose and cleaning the air gap don’t stop the gurgling, the blockage may be farther in the drain or the vent may be obstructed.
What Not to Do
- Do not snake vents blindly from the roof or through the sink without knowing the layout; call a professional if access is unsafe.
- Do not pour strong chemical drain cleaners into a trap or disposal—these can damage seals and are dangerous if mixed with other chemicals.
- Do not work on the disposal or electrical connections without shutting off power first.
When to Call a Professional
- If several fixtures gurgle or back up, indicating a main sewer line or vent problem.
- If you can’t access the clog or vent safely—roof access, attic work, or complex home vent layouts are best left to a plumber.
- If sewage is backing into the sink, if there’s a strong sewer smell, or if repeated DIY attempts fail to fix the problem.
Safety Notes
- Always turn off power to the garbage disposal at the breaker before working on it.
- Use gloves and eye protection when handling drain debris.
- Avoid roof or attic work unless you have proper training and fall protection—call a professional instead.
- Keep chemical drain products out of reach and never mix them with other chemicals.
Common Homeowner Questions
- Why does it only gurgle when the dishwasher runs? The dishwasher pumps a large volume of water quickly, so any restriction or blocked vent is more likely to cause pressure swings then.
- Can I keep using the dishwasher until it’s fixed? If water is backing up into the sink or disposal, stop using it and call a plumber; occasional gurgles alone may be okay to monitor briefly.
- Will a simple snake fix this? If the clog is in the sink trap or nearby drain, yes; if the issue is a blocked vent or farther in the main line, a professional is usually needed.