What You Need Before You Start

Installing an InSinkErator garbage disposal takes between one and three hours if you have basic plumbing skills and the right tools. You will need a screwdriver (Phillips and flathead), an adjustable wrench, plumber's putty, a bucket to catch water, and possibly a hacksaw if your drain lines need cutting. Check whether your sink has a three-bolt or EZ mount system — most newer InSinkErator models use EZ mount, which is faster. If your current disposal is being replaced, you will need to disconnect the old unit first.

Before you buy the disposal, measure the space under your sink. InSinkErator makes compact models for tight cabinets and standard models for typical installations. The power outlet under the sink matters too — if there is no outlet, you will need an electrician to install one, which adds cost and time. If you are uncomfortable with electrical work or plumbing, hiring a plumber costs between $150 and $300 but removes the risk of leaks or electrical problems.

Key Takeaways

  • Turn off the power at the breaker before you touch any wiring, and keep the power off until the disposal is fully installed and tested.
  • The mounting ring holds the disposal in place — tighten the three bolts evenly in a star pattern to avoid tilting and leaks.
  • Plumber's putty seals the sink flange to the sink itself and prevents water from leaking into the cabinet.
  • The discharge tube connects the disposal to your drain line and must slope downward slightly so water flows toward the main drain.
  • Test the disposal with cold water running before you use it with food waste, and check under the sink for leaks at all connection points.

Removing the Old Disposal (If Replacing)

Turn off the power at the circuit breaker and unplug the disposal if it has a plug. Place a bucket under the unit to catch any remaining water. Loosen the discharge tube where it connects to the drain line using an adjustable wrench, then remove the tube. Unscrew the three bolts on the mounting ring in a star pattern (top, bottom-left, bottom-right) so the weight distributes evenly and the unit does not drop suddenly.

Once the bolts are loose, support the disposal with one hand and unscrew the final bolt. Lower the unit carefully into the bucket or onto a towel. If the sink flange (the ring that sits in the drain hole) is stuck, tap it gently from below with a rubber mallet. You may need to scrape old putty away with a flathead screwdriver. Clean the sink opening thoroughly before installing the new disposal.

Installing the Sink Flange and Mounting Ring

Roll plumber's putty into a rope about the thickness of a pencil and press it around the underside of the sink flange. Push the flange down into the drain hole from above, pressing firmly so the putty creates a watertight seal. From below the sink, slide the rubber gasket onto the flange, then the metal mounting ring. Hand-tighten the three bolts first — do not use a wrench yet.

Once all three bolts are hand-tight, use an adjustable wrench to tighten them in a star pattern: tighten the top bolt a quarter turn, then the bottom-left, then the bottom-right, then repeat. This keeps the mounting ring level and prevents the flange from tilting, which causes leaks. Tighten until the ring is snug but not so hard that you strip the bolts. Wipe away any excess putty that squeezes out around the flange.

Connecting the Disposal to the Mounting Ring

Align the disposal unit with the mounting ring so the three tabs on the disposal line up with the three slots on the ring. Push the disposal up and turn it clockwise until it locks into place — you will feel it catch. The disposal should hang securely and not wiggle. If it feels loose, remove it and check that the mounting ring bolts are tight enough.

Once the disposal is locked in, connect the discharge tube to the outlet on the bottom of the disposal. This tube carries water and waste to your drain line. Tighten the connection by hand first, then use a wrench to snug it — do not over-tighten, as the fitting can crack. The discharge tube should slope downward toward the main drain so gravity helps water flow out.

Connecting the Drain Line and Testing for Leaks

Attach the discharge tube to your existing drain line using a slip nut (the large nut that holds the connection). If you are connecting to a P-trap, loosen the slip nut on the P-trap, slide the discharge tube into the opening, and tighten the slip nut hand-tight, then snug it with a wrench. If the tube does not reach, you can buy an extension tube at any hardware store — cut it to length with a hacksaw if needed.

Before you plug in the disposal, fill the sink with cold water and turn on the disposal to check for leaks. Watch under the sink for drips at the flange, the discharge tube connection, and the drain line connection. If you see water dripping, turn off the disposal when ready and tighten the leaking connection. Small drips often stop after a few minutes as the putty or gasket settles, but steady streams mean the connection needs to be tighter or the gasket needs to be replaced.

Electrical Connection and Final Setup

If the disposal has a power cord, plug it into the outlet under the sink. If it is hardwired (no cord), an electrician must connect it to the circuit breaker. Do not attempt hardwiring yourself unless you have electrical experience — mistakes can cause shock or fire. Once power is connected, test the disposal with the wall switch or the air switch (if your sink has one) to make sure it runs smoothly and stops when you release the switch.

Run cold water while the disposal is on for a few seconds to flush the system. Do not put food waste in the disposal for the first 24 hours — let the plumber's putty cure fully. After that, run cold water before and after each use, and never put fibrous materials like celery, corn husks, or potato peels down the disposal, as they can jam the blades.

Troubleshooting Common Installation Problems

If the disposal leaks from the flange, the putty seal is broken. Turn off the power, remove the mounting ring bolts, and pull the disposal down. Scrape away the old putty, explore fresh putty, and reinstall the mounting ring. If the discharge tube leaks, tighten the slip nut or replace the rubber gasket inside the connection. Leaks at the drain line connection usually mean the slip nut is loose — tighten it with a wrench while supporting the P-trap with your other hand so you do not bend the pipe.

If the disposal does not turn on, check that the power is on at the breaker and the outlet is working by plugging in a lamp. If the outlet is dead, the circuit may have tripped — flip the breaker off and back on. If the disposal hums but does not spin, something is jamming the blades. Turn off the power, look into the drain with a flashlight, and remove any object with tongs or pliers — never put your hand in the disposal. If none of these steps work, the motor may be faulty and the unit may need to be replaced.

Frequently Asked Questions

Do I need a plumber to install an InSinkErator disposal?

No, but a plumber is worth the cost if you are not comfortable working under a sink or if you have no electrical outlet available. The installation itself is straightforward — the main risks are leaks from loose connections and electrical mistakes. If you have replaced a disposal before or are handy with basic tools, you can do it yourself.

Can I install a disposal in a sink that does not have one?

Yes, but you need a drain hole in the sink. If your sink has a single drain and you want to add a disposal, you can use that hole. If your sink has two drains and you want to add a disposal to one side, you will need to cap off the other drain with a plug. Some sinks have a knockout plug already in place — you can remove it to create a new hole for the disposal.

What if water backs up into the other side of my double sink?

This usually means the drain line is clogged or the P-trap is blocked. Turn off the disposal and run a plumbing snake through the drain to clear the blockage. If the backup happens only when the disposal is running, the discharge tube may not be connected properly to the main drain line — check that it is fully inserted into the P-trap and the slip nut is tight.

How long does plumber's putty take to dry?

Plumber's putty does not fully cure for 24 hours, though it sets enough to hold the flange in place within an hour. Wait a full day before running the disposal with food waste. If you see water leaking from the flange before 24 hours have passed, it usually means the mounting ring bolts are not tight enough — tighten them and wait another few hours.

Can I install the disposal myself if I have never done plumbing before?

Yes, if you follow the steps carefully and take your time. The most common mistakes are not tightening the mounting ring bolts evenly (which causes leaks) and not connecting the discharge tube to the drain line properly. Watch an InSinkErator installation video for your specific model before you start, and do not hesitate to call a plumber if something does not fit or feel right — a $300 service call is cheaper than water damage to your cabinets.