Quick Answer:
If water appears only while the disposal runs, vibration is likely opening a loose joint, loosening a clamp, or forcing water through a crack or bad seal. Start with a careful inspection, then run the unit briefly with a steady stream of water while watching under the sink to see where the drip begins. If tightening simple fasteners doesn’t stop it, or you see damage to the housing or flange, turn the power off and call a pro.
Why This Happens
- Vibration from the motor can open small gaps at the sink flange, mounting ring, discharge connection, or hose clamps that are tight when the unit is off but leak while running.
- A cracked disposal housing or a failed internal seal will often only force water out when the unit shakes during operation.
- Improper installation or loose mounting hardware lets the unit move just enough under load to spray or drip at a joint.
- Recent work on the disposal can leave fittings under-torqued or seals improperly seated; if you recently changed the unit, check that work first (see Leak after replacing disposal).
Step-by-Step What to Do
1. Prepare safely
- Turn off the disposal at the wall switch and unplug it or switch off its circuit at the breaker before putting your hands or tools under the sink.
- Place a flashlight and a bucket or towels under the unit to catch water.
2. Do a static inspection
- Look for wet spots on the sink flange, mounting ring, discharge elbow, trap, and dishwasher hose connection.
- Feel for loose screws or a wobbly mounting ring by gently trying to move the disposal from the sink. Don’t force anything.
3. Tighten obvious fasteners
- Tighten the dishwasher hose clamp and the discharge elbow nut using the correct screwdriver or wrench. Small leaks at clamps often stop with a modest tightening.
- If the mounting ring is adjustable and appears loose, follow the manufacturer’s instructions to snug it. If you’re not sure how, stop and call a pro.
4. Run a safe test to reproduce the leak
- Have a helper stand at the switch, or use the switch yourself while keeping hands clear. Turn the power back on or flip the breaker to the on position only for the short test.
- Run a steady stream of cold water down the sink and turn the disposal on for just a few seconds while you watch under the sink. Run the disposal briefly with a steady stream and watch for leaks that appear only under vibration.
- If you see water spraying or a leak appear, note the exact location: at the flange, around the housing, at the discharge, or from a hose.
5. Decide next steps based on what you find
- If the leak is from a clamp or a loose discharge joint, re-tighten and re-test.
- If the leak comes from the sink flange, the mounting seal may need reseating—this can require removing the disposal and resealing the flange with plumber’s putty or a replacement gasket.
- If water is escaping the body of the disposal or you find a crack, don’t try to patch it—replace the unit.
What Not to Do
- Do not assume a running-only leak is harmless; vibration leaks can progress quickly.
- Do not put your hand into the disposal or reach past the splash guard while testing or inspecting. Always disconnect power first.
- Do not run the disposal without water; that stresses seals and can damage the unit.
- Do not attempt welding, gluing, or other heat repairs on the metal housing or electrical parts under the sink—those are unsafe and unreliable.
When to Call a Professional
- Call a plumber or appliance tech if the leak continues after simple tightening, if the mounting hardware needs removal or replacement, or if the sink flange must be resealed.
- If you see Water spraying from disposal housing or discover a crack in the metal, stop using the unit and get professional help—housing failures mean replacement is often required.
- If you are unsure about turning off the power, working on plumbing connections, or removing the disposal, a pro will do the job safely and prevent further damage.
Safety Notes
- Always disconnect power before putting hands or tools near the unit.
- Use eye protection and gloves when working under the sink to guard against splashes and sharp edges.
- Keep children and pets away while you test and work on the disposal.
- Do not rely on chemical drain cleaners to fix leaks—they won’t and can damage the disposal and seals.
Common Homeowner Questions
- Why does it only leak when the disposal runs?
Vibration opens a weak joint or forces water through a failing seal or crack that is otherwise closed when the unit is still. - Can I fix a running-only leak myself?
Often yes for loose clamps or fittings; stop and call a pro for flange reseals, housing cracks, or electrical concerns. - Is it safe to keep using the disposal until I can fix it?
No—running a leaking disposal can worsen the damage and risk water hitting electrical parts. Test briefly to locate the leak, then stop and repair it.