New garbage disposal installed under kitchen sink.

New Kitchen Appliances:

Installing A Kitchen Food Waste Disposal

In This Article: Related Articles:
Skill Level: 2-3 (Basic to Intermediate) Time Taken: About 2 Hours

By , Editor


I was recently asked to install an In-Sink-Erator food waste disposer in a new house. Years ago when I worked in resort maintenance I had replaced several disposers. Replacing an In-Sink-Erator disposer is pretty easy; installing a new one is more work because the mounting bracket needs to be installed and the drain pipes need to be figured out.

In-Sink-Erator seems to have a lock on the market for garbage disposals. ISE is the only brand I've replaced or installed, and I see the brand everywhere. The units I've replaced have all been in ski resort condos, and skiers are not known for being gentle on rental properties, so it's no surprise that some ISE disposers conk out after two decades.

Note that these appliances do not come with a power cord. For a replacement, the cord is simply transferred. For a new disposer, you can buy a cord specifically for ISE disposers, or make your own from a male plug and flexible cable of appropriate size.

The plumbing before the disposer was installed. The horizontal connection is quite high up and will need to be lowered.


A basic ½HP In-Sink-Erator waste disposer, about $65 at Home Depot.


I removed the dishwasher drain line.


I removed the drain pipes between the sink baskets and the P-trap. This will all need to be re-built after the disposer is installed.


This tool is a basket wrench. It's used to hold the sink basket in place while the big locking nut (below the sink) is turned.


I placed the basket wrench in the drain opening...


...while I grabbed the basket nut with a pair of 18" Channel-Lock pliers. On many older houses it is impossible to remove this big nut, so it needs to be broken or cut off.


The basket was removed from the sink opening.


I removed the old plumber's putty from the hole and cleaned the rim (with Windex) so the silicone would stick.


I removed the mounting bracket from the disposer. It's only held loosely while in the package.


There are 3 screws (actually more like threaded rods) that hold the bracket together. These screws were backed out to gain access to the snap ring.


The red arrow points to the snap ring.

The snap ring was pried off with a twist of a screwdriver. 


Then I took the bracket apart.


I applied a heavy bead of clear silicone, in spite of In-Sink-Erator's instructions to use plumber's putty. Silicone is an excellent adhesive and will probably bond the bracket to the sink even if the screws come loose.


I made three laps around the hole with the silicone, just to be sure I had complete coverage. It's easier to remove the excess than to go back later and fix a leak caused by insufficient caulk.

I placed the top flange in the hole.

This is a bit awkward to do with one person, and it's even more difficult to photograph.

I placed the fiber washer and triangular-shaped backing ring on the stem of the top piece, then I slipped the mounting ring (which has the three screws) up there and installed the snap ring. That was kinda tricky to do by myself. The instructions say to place a heavy weight in the sink to hold the flange from moving, but that would smear the silicone making it much more difficult to remove later. Installing In-Sink-Erator disposal mounting bracket in sink.

AFTER I did this, I read in the instructions that placing a couple of wide rubber bands around the stem will prevent the parts from falling off. D'oh!

 I tightened the screws that clamp the assembly together.

This is a good point to take a break, as the silicone will start to harden and reduce the risk of messing up the seal (by moving the bracket slightly) when the appliance is attached to the bracket.

Dishwasher Connection:

Note how the dishwasher connection is blocked off. 


I used a hammer and a screwdriver to remove this knock-out plug.

Don't leave this chunk of metal inside the disposer or it'll make an awful racket.


The next step was to install the dishwasher drain hose on the disposer inlet, but the drain hose had already been cut to the smallest size, for a 5/8" O.D. tube. I had purchased a connection adapter rubber boot, just in case, but the inlet to this boot is soft rubber. The hose has to clamp onto something rigid, so I cut a short length of ½" copper pipe, which has an outside diameter of about 5/8".

I attached the dishwasher drain hose to the copper pipe, and the pipe was attached to the adapter boot by a spring clamp. The boot was mounted to the disposer by an automotive-type hose clamp.


Electrical Connections:

It's important to note that the usual method of controlling a waste disposer is by plugging the appliance into a switched outlet that is installed beneath the sink.

No Switched Outlet?

Disposers do not have an on/off switch, so if there's not already a switched outlet below your sink, you'll need to have that installed. In older houses I have seen this approach:

  • Run a cable to the cabinet below the sink.
  • Install a metal surface-mount box just inside the cabinet door for the switch.
  • Connect the power cord to the switch.
  • Note that armored cable (which has a flexible metal sheath) or flexible conduit may be required.

This is basic electrical work, if the house has a basement or crawl space. Without access from below, getting power to the space under the sink can be challenging. The proper approach is to fish a cable downward from one of the outlets over the counter, and install an "old work" box. This can be a complex job that requires some specialty tools and skills. For some people the easiest solution is to have an electrician install the switched outlet. 

The disposer does not come with a power cord, so I bought one made by In-Sink-Erator. A cord could be made just as well, as long as everything is rated for the proper current level. The ISE cord uses 16-3 wire, so I would use at least that size, probably bigger (such as 14 or 12 gauge wire) and a male plug rated at 15 amps.

While it's tempting to use plain NM-B building cable (which is meant to be hidden inside walls), the proper cable is something rated for extension cord use, at the very least. Most hardware stores and home centers carry a wide variety of flexible-wrapped 3-conductor cables rated for applications that are exposed to occasional movement. Some building codes may require flexible conduit or armored cable for this type of exposed wiring.

I removed the access cover and installed the cable clamp provided with the cord. There is a black wire and a white wire inside the cover.


I threaded the power cord through the cable clamp and tightened the screws.


I connected the green ground wire to the ground screw and connected the hot and neutral lines.


How The Disposer Connects To The Mounting Bracket:

ISE disposers use a clever mounting technique. When an old ISE disposer is being replaced with a new unit, the old mounting bracket can remain attached to the sink.

The lower mounting ring (which is part of the disposer) has 3 tabs that grab the mounting bracket.
  • Arrow 1 points to the flange.
  • 2 is the tab that grabs onto the flange.
  • 3 is the "ear" that is used to rotate the lower ring.
As the lower ring is turned, each tab grabs onto a flange (red arrow).
The flanges are actually ramps, as this side view shows.

If a disposer needs to be removed, simply tapping on the ear with a hammer will quite easily loosen the lower mounting ring.


I attached the disposer to the mounting bracket. This is kinda tricky because it's difficult to get all 3 tabs to catch on the ramps while simultaneously holding the disposer up with one hand.

Having a helper makes this easier.

Before tightening, the disposer may need to be rotated so the drain opening points toward the drain pipe.

I tightened the locking ring with the little wrench provided with the disposer. (The wrench is for turning the shaft manually in case the disposer becomes jammed during use.)


Plumbing Connections:

I connected a 12" long tail piece (1½" diameter, like all kitchen drain pipes) to the outlet of the disposer. ISE provides a special black plastic gasket that fits into the end of the T-shaped tail piece.


The red arrows point out the places where the original plumbing needed to be changed.

Note how the T-connector junction piece (between the two arrows) is much lower than the tailpiece below the left sink basin. I had to buy a longer tailpiece for the left basin, and I needed an extension tube to connect the tee to the trap.

Originally there was a dishwasher tee fitting below the main tee fitting, but I removed that.

 Normally a dishwasher is drained into the disposal. I guess the reason is that any food waste in the dishwasher can be ground up later on.

Note how the tail piece works: The pipe has a T-shaped flange, and a soft plastic gasket is placed between the flange and the bottom of the sink basket. The metal nut (which comes with the sink basket) clamps the assembly together. Plastic nuts also work here, but I prefer metal.


The trap was the last piece of drain that I installed.

For more information on drain plumbing, read Installing A Sink Drain.


After the silicone had dried, I cut it away with a sharp knife. It's best to wait a full day before doing this, because the silicone in the middle of the bead can still be soft even though the outside is hard.

This is the biggest drawback to using silicone under the sink flange instead of the usual plumber's putty. Removing excess putty is easier, but putty leaks too easily. I've never had a siliconed sink connection leak. Breaking such a connection apart isn't so easy, however, but that should never be necessary.


The completed installation.


The view from the top.

If the rubber splash guard ever gets damaged (I've seen that happen) it can easily be replaced by removing the disposer from the mounting bracket, snapping a new splash guard in place, and re-installing the disposer. Replacing a worn rubber guard is a good idea when selling your house because it makes the unit look like new, at least from above.


What Evil Lurks In The Heart Of A Food Waste Disposer?

If you've ever wanted to know how a garbage disposal works, don't go sticking your hand inside one to find out. Look at this picture instead:

The primary components in a disposer are the hammers (arrow 1) and the slots in the stationary body (arrow 2). All of the residential disposers I've seen have two hammers. 

When the power is applied, the base rotates and the food particles are thrust (by centrifugal force) towards the edge. When a piece of food gets stuck in a hole, it stops briefly and then gets whacked by a hammer. Chunks small enough to fit through a hole are washed downstream.

If there is nothing in the disposer, the hammers don't flail around, and the unit makes very little noise. 


Disposal Problems:

I've seen a few disposal problems over the years:

Jammed shaft: ISE supplies a small Allen wrench (they call it a "wrenchette") to rotate the motor shaft if the unit becomes jammed. It's pretty easy to jam up a disposer by being too aggressive with the waste. Tough materials like the shells from shrimp will not get ground up, and too much of this can jam the disposer. Getting a piece of broken glass in the disposer is another common cause of jamming.

Overload: If an ISE disposer won't run, first make sure the shaft is free to spin (using the wrenchette) and try resetting the circuit breaker on the bottom. A small red button will pop out if the motor jams and becomes overloaded. Leaving the power applied to a stalled electric motor WILL overload it.

Plugged Disposer: Years ago I lived in an apartment and I put a lot of onion skins in the disposer. They mostly didn't go down. I had to reach into the disposer (unplug the darned thing when you do this, don't be foolish) and pick out a pile of wet onion skins. Then I removed the sink trap and picked out a pile of slightly-shredded onion skins.

Mildew Smell: In that same apartment, the disposer had a nasty mildew smell. I tried the usual remedy... baking soda... but that did nothing. I filled the unit with ice cubes and ground them up, but still no improvement. I looked inside with a flashlight and I determined that there was fungal growth on the top surfaces of the chamber, which doesn't get a lot of scraping from normal use. I didn't own a lot of tools then, so I had no way of applying chlorine bleach inside the disposer and make it spray upwards. So I filled the unit with ice cubes, and when I turned it on I poured some full-strength bleach inside, hoping it would get splashed onto the "ceiling" of the chamber. It didn't help much. In hindsight, a better approach would be to dip some sort of bottle brush in bleach and scrub the insides. Failing that, removing the unit would allow you to reach the insides much easier. I solved the problem by complaining to the apartment management, and after a few days they replaced the disposer.


Maintenance: Pouring ice cubes into the disposal is the usual way of cleaning gunk and debris from the inside. Just don't pack it too full... the disposer can stuff ice shavings into the drain pipe so tightly that the pipe fittings leak. ISE recommends occasionally grinding hard material such as small bones and fruit pits.


Tools Used:

  • Adjustable Wrenches
  • 18" Channel-Lock Pliers
  • Sink Basket Wrench
  • Basic Hand Tools

Materials Used:

  • Disposer, In-Sink-Erator ½HP
  • Power Cord
  • Dishwasher Connector Boot
  • Plumbing Drain Parts
  • Clear Silicone Caulk


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Copyright © 2002, 2005

Written April 23, 2002
Revised (Formatting) January 5, 2005