Quick Answer:
If water appears around the top rim of the sink opening where the disposal meets the sink, the flange seal is likely failing. Stop using the disposal, turn off power at the breaker, and run a simple sink-fill test to confirm whether water is bypassing the seal at the top. If the test shows seepage, the flange should be reseated or the seal replaced rather than patched with caulk.
Why This Happens
A flange seal can fail because the plumber’s putty or rubber gasket compresses, shifts, or dries out over time. Movement from the disposal or sink, corrosion of the mounting ring, an improperly seated flange at installation, or a cracked sink opening can also let water run past the seal. If the leak only happens when the dishwasher runs, that points toward backflow or a separate hose connection issue and you may want to review the information on Leak only when dishwasher drains.
Step-by-Step What to Do
Step 1: Prepare and shut off
- Turn off power to the disposal at the circuit breaker — do not rely solely on the wall switch.
- Place a bucket and towels under the sink to catch any water.
- Clear the cabinet so you can work and see the mounting assembly from below.
Step 2: Do the sink-fill test
- Seal the overflow and plug the sink, then fill the basin about halfway with water.
- Check the flange area for wetness at the top edge of the sink opening. Check the flange seal by observing seepage around the sink opening while the basin is full.
- Look from above and below while the sink is full to see whether water is tracking down the outside of the flange or coming from under the mounting assembly.
Step 3: Inspect the mounting and seal from below
- With power off, look up at the sink flange from below. Inspect the mounting ring, gasket, and any plumber’s putty for signs of separation, cracks, or hardened material.
- Check that the disposal is properly supported and that the mounting bolts or snap-ring are tight and evenly seated.
- If you see moisture on the flange itself but the mounting looks solid, the seal material may have failed and needs replacement.
Step 4: Reseat or replace the flange seal
- If you can safely do the work: support and disconnect the disposal following manufacturer instructions (power off, unplug or ensure breaker is off) and remove the disposal from the sink mounting.
- Clean all old putty or gasket residue from the sink opening and flange. Replace with fresh plumber’s putty or a new rubber gasket per the manufacturer’s recommendation, and reinstall the flange so it sits squarely in the sink opening.
- Reinstall the mounting hardware and tighten evenly so the flange is compressed uniformly. Do not overtighten a plastic sink or you may crack it.
Step 5: Test again and monitor
- Restore power and water, then repeat the sink-fill test and run the disposal briefly with water flowing to check for leaks.
- If the leak appears only when the dishwasher runs or near the hose inlet, inspect the dishwasher hose connection or the inlet on the disposal — you may find more details under Disposal leaks at dishwasher inlet.
- Watch the area for several days to confirm the repair holds under normal use.
What Not to Do
- Do not rely on caulk as a primary fix for a flange seal; proper seating matters.
- Do not run the disposal while testing for a suspected flange leak; that can push more water into areas and hide the source.
- Do not put your hand into the disposal or attempt internal repairs without verifying the power is off at the breaker.
- Do not overtighten metal parts on a fragile sink — excessive force can cause cracks that worsen leaks.
When to Call a Professional
- Water continues to leak after you’ve reseated or replaced the seal.
- There is visible corrosion, cracks in the sink, or damaged mounting hardware that needs replacement.
- Leaks are causing water damage inside the cabinet or to ceilings below.
- You are uncomfortable working near plumbing or electrical connections under the sink.
Safety Notes
- Always cut power at the breaker before working under the sink or removing the disposal.
- Wear gloves and eye protection when handling old plumber’s putty or working in confined spaces.
- Support the disposal when loosening the mounting to prevent it from dropping.
- Use a bucket and towels to contain spills and prevent splash into electrical areas.
Common Homeowner Questions
- How quickly should I stop using the disposal if I suspect a flange leak? Stop immediately and turn off power; running it can worsen the leak.
- Is replacing the flange seal something a homeowner can do? Yes, if you are comfortable shutting off power, supporting the disposal, and following basic reinstallation steps.
- Will plumber’s putty always stop a leak? No. Putty must be applied and seated correctly; if the flange or mounting hardware is damaged, the seal won’t hold.