How the top of a disposal seals
A disposal hangs from a metal flange that sits in the sink's drain hole. The flange is sealed to the sink with plumber's putty or a rubber gasket, and a mounting ring underneath clamps it tight. The disposal then locks onto that ring with a twist.
Every time the disposal runs, it vibrates. Over years of use, that vibration can loosen the mounting screws, compress or dry out the putty, and let water seep between the flange and the sink. A disposal that was jammed and forced free can also shift the mount. The result is a drip that shows up on the top of the unit, often only when the sink is full.
Confirm the leak is really at the flange
Power off and dry everything
Turn off and unplug the disposal, then wipe the unit, the connections and the cabinet floor completely dry.
Fill the sink partway
Close the drain stopper and put a few inches of water in the sink bowl above the disposal.
Watch with a flashlight
Look at the seam right under the sink. A flange leak shows water beading at the top edge of the mount within a few minutes.
Rule out the other spots
If the top stays dry, check the dishwasher hose, the drain elbow and the bottom of the unit instead.
Where the water shows up
| Location | Usual cause | Typical outcome |
|---|---|---|
| Top seam under the sink | Loose mount or failed putty or gasket | Reseal and retighten the flange |
| Side, at the dishwasher hose | Loose clamp or cracked hose | Tighten or replace the hose |
| Side, at the drain elbow | Worn gasket or loose flange bolts | Replace the gasket |
| Bottom of the housing | Failed internal seals | Usually replace the unit |
How a flange leak is fixed
A plumber typically removes the disposal from its mounting ring, loosens the ring, lifts the flange, cleans off the old putty, and reseats the flange with fresh putty or a new gasket before reassembling and retightening everything evenly. If the flange or ring is corroded or bent, those parts are replaced. On some sinks, particularly thinner stainless models, the flange may need extra attention to sit flat.
If the disposal is old and the plumber is already removing it, it is fair to ask whether it makes sense to replace it at the same visit, especially if it has other problems.
What affects the cost
- Parts
- Putty or gasket only, or a new flange and ring
- Access
- Crowded cabinets and tight drain layouts take longer
- Condition
- Corroded bolts or a damaged sink opening add work
- Cabinet damage
- Water-damaged cabinet floors are a separate repair
Questions to ask a plumber
- Is the leak definitely at the flange, or somewhere else?
- Will you reuse the flange or replace it?
- Is the disposal itself in good enough shape to remount?
- Will you test with a full sink before you leave?
Common questions
Can I just tighten the mounting screws?
Sometimes that slows the leak, but if the putty or gasket has failed, it will usually come back. Turn the power off before reaching under the sink at all.
Why does it only leak when the sink is full?
A full sink puts water pressure on the flange seal. When the sink is empty, little water sits there to escape.
Does a flange leak mean I need a new disposal?
Not usually. The disposal itself is often fine; it is the seal between the flange and the sink that needs redoing.
General information for Fullerton, not a quote or professional advice. In an emergency, call 911.