Quick Answer:
A new gurgling noise when the sink drains usually means air is being pulled through the trap or a vent is restricted. Check venting by listening while other fixtures run, confirm the trap arm slope, and make sure the disposal outlet isn’t creating a double-trap or a long horizontal run that traps air. If gurgling continues when other fixtures run, call a plumber.
Why This Happens
- Trap siphoning: If the trap or trap arm lets water flow in a way that pulls air through the trap, you hear gurgling as air and water move.
- Blocked or inadequate venting: Vents let sewer air escape and allow air into the drain so water flows smoothly. A restricted vent can cause gurgling when the system tries to equalize pressure.
- Poor discharge layout: A disposal outlet that forms a double-trap, or a long, flat horizontal run between the disposal and the trap/vent, can hold pockets of air and cause gurgling.
- Installation changes: Replacing or repositioning the disposal can change how the tailpiece connects, altering slope or creating a low spot that collects air.
Step-by-Step What to Do
1. Turn off power and run a quick safety check
- Unplug the disposal or switch off the breaker before reaching under the sink.
- Open the cabinet, use a flashlight, and look for loose or obvious misalignment where the disposal meets the sink tailpiece and trap.
2. Reproduce the noise and compare fixtures
- Run the sink and disposal as usual, then listen closely under the cabinet to locate the sound.
- While the sink is draining, have someone flush a toilet or run a washing machine drain nearby. If the sink gurgles when another fixture runs, that points to a vent or shared drain pressure issue.
3. Check the trap and trap arm slope
- Look at the trap arm (the horizontal pipe from the trap to the wall). It should slope downward toward the wall roughly 1/4 inch per foot. A flat or uphill run can trap air or slow flow.
- If the trap arm is too long or flat, shorten it or re-pitch it so water runs freely to the vented stack.
4. Inspect the disposal outlet for double-trap or long horizontal runs
- Ensure the disposal tailpiece drops into the trap without creating an extra trapped bend below the normal P-trap. A second trap pocket will hold air and send gurgles back up.
- A long, nearly level horizontal section between the disposal outlet and the trap can hold an air pocket. Re-route or shorten that run so it has a steady downward slope.
5. Test after adjustments
- Reassemble, restore power, and run water and the disposal while watching and listening. Repeat the toilet/washing machine test to see if the venting-related gurgle is gone.
- If the noise is reduced but not gone, note when it happens (only with the disposal, or whenever other fixtures run) to give clear information to a technician if you call one.
What Not to Do
- Don’t assume gurgling is normal after an install—ignoring siphoning can dry the trap and allow sewer gas into the home.
- Don’t leave a persistent gurgle uninvestigated; if gurgling happens when other fixtures run, a plumber is appropriate.
- Don’t put your hand or an uninsulated tool into the disposal without power completely off and the unit immobilized.
- Don’t force plumbing parts together if fittings won’t seat properly; leaking or misaligned connections make problems worse.
When to Call a Professional
- If the sink gurgles whenever other fixtures run (toilet, washer), that suggests a venting or main drain problem—call a plumber.
- If you can’t get a proper slope on the trap arm without cutting pipes or changing fittings, call a plumber for a clean, code-compliant repair.
- If you notice persistent sewer smell, inspection or repair may be needed—see Odor after disposal replacement.
- If water is backing up into other fixtures or you suspect flow between lines, review by a pro is warranted—see Cross-flow after disposal install.
Safety Notes
- Always disconnect power to the disposal at the wall or breaker before working under the sink.
- Never put your fingers or tools into a disposal unless the motor is off and you can see the obstruction. Use long tools designed for plumbing work if needed.
- Use proper eye protection and gloves when working with plumbing connections and when running tests with multiple fixtures.
Common Homeowner Questions
- Why did the gurgling start after the new disposal? A repositioned tailpiece or different outlet angle can change trap slope or create a pocket of air—those layout changes commonly cause gurgles.
- Can I fix vent problems myself? Minor roof vent clogs (leaves, debris) can sometimes be cleared safely, but accessing roof vents can be hazardous—call a plumber if you’re unsure.
- Will running more water stop the gurgle? Temporary increases in flow can mask the noise, but they won’t fix siphoning, double-traps, or blocked vents; those require proper adjustment or repair.