Replace a Garbage Disposal

Goal

Replace a failed garbage disposal with a new unit. Common job: the existing disposal hums but doesn't grind (motor seized), leaks at the casing (housing rusted through), or stopped entirely (motor failed). 45 - 60 minute job; the hard part is the awkward under-sink position.

Prerequisites

• New disposal matched by:
  • HP (1/3, 1/2, 3/4, 1)
  • Mounting style (3-bolt vs Quick Connect - InSinkErator's snap-lock vs others)
  • Drain configuration (1-1/2" or larger)
• New mounting hardware (often included with new unit)
• Plumbers putty OR silicone
• Channel-lock pliers, screwdriver, allen wrench
• Bucket, towels
• 45 - 60 minutes

Steps

1. Cut power at the disposal switch + breaker. The disposal is on a dedicated branch circuit in most installs.
2. Disconnect under-sink electrical. The disposal will have either a hardwired cable connection at a junction box OR a plug into an outlet. Disconnect appropriately.
3. Disconnect drain plumbing. Loosen the slip-nut on the drain pipe at the disposal outlet. Bucket below.
4. For dishwashers (if connected): disconnect the dishwasher drain hose at the disposal's barbed inlet.
5. Support the disposal from below. It's heavy (10 - 20 lb depending on HP) AND it will fall.
6. Unlock the mounting assembly. Turn the lower mounting ring counter-clockwise. The disposal drops free.
7. If replacing with the same brand + mount system: the upper sink-flange assembly stays. Skip to step 11.
8. If replacing with a different brand: remove the upper flange too. Loosen the snap ring + the screws holding it.
9. Clean the sink rim of old putty residue.
10. Install the new upper flange. Apply plumbers putty (or silicone) underneath the rim. Press firmly into place; tighten the snap ring + screws to compress the gasket evenly.
11. Pre-wire the new disposal at the electrical strain relief BEFORE mounting. Easier than working under the sink with the disposal in place.
12. Knock out the dishwasher inlet plug (if the customer has a dishwasher). Most new disposals ship with a plastic plug - required to be removed to allow dishwasher drainage. Easy to forget; if you do, customer's dishwasher won't drain.
13. Mount the new disposal. Lift, align with the upper flange, twist clockwise to lock.
14. Connect dishwasher drain hose (if applicable). Hose clamp on the barbed inlet.
15. Connect main drain pipe to the disposal outlet. Slip nut tightened by hand + slight wrench-snug.
16. Restore power. Run water, switch on the disposal. Listen for:

• Smooth motor sound (not grinding metal-on-metal)
• Water flowing through cleanly (no leaks at any connection)
• Disposal switch operates correctly

Verification

• Disposal runs smoothly under full water flow
• No leaks at the sink flange (look up at the rim from under the sink)
• No leaks at drain or dishwasher connection
• Dishwasher drains correctly (run a short rinse cycle if available)
• Customer can demonstrate operation

Troubleshooting

• Leak at the sink flange after install: putty didn't seat or wasn't enough. Pull + redo with fresh putty/silicone.
• Disposal won't start (no hum): reset button on the bottom popped during testing. Press to reset. Then verify the breaker AND the switch.
• Disposal hums but won't spin (immediate): foreign object stuck in the impeller. Cut power; reach in carefully with pliers (or the disposal wrench tool, hex shape on the bottom).
• Customer's dishwasher won't drain: the inlet plug wasn't removed. Pull disposal back out; tap out the plug with a screwdriver from the inside; reinstall.

References

• Manufacturer install instructions (InSinkErator, Waste King, Moen)
• IAPMO Uniform Plumbing Code, Chapter 8 (Indirect Wastes)
• Manuall internal: Smelly Drain - Diagnostic Tree, Annual Whole-Home Plumbing Inspection