Installing a new garbage disposal requires working with electricity and plumbing. If you are uncomfortable with working with either, call a professional to do the work. However, in terms of complexity with either of those skill sets, I would rate it as moderately difficult, again depending on your experience as a handy man. If you have installed or change out an old electrical outlet, or change out a P-trap, this project should not be difficult for you.
In order to install a garbage disposal under the kitchen sink, you will need access to a power source near the area. If you do not have access to a direct outlet, you will need to install a new one to plug it in.
Before you begin any project, check your local building codes because some areas actually do not allow garbage disposals because of sewer capacities. Furthermore, they may require an air gap between the disposal and the dishwasher.
Another consideration before you begin is whether or not you are on a septic system. If so, purchase a unit that is specifically designed to use with a septic tank.
Deciding on a Garbage Disposal
Garbage disposals below ½ horsepower are not really very good at doing anything except making a lotCredit: Amazon.com of noise. Look for a unit with insulation to reduce the noise from the grinding. Consider purchasing one with 1 horsepower if there are more than two people in your home.
There are two basic types of disposers:
- Continuous feed
- Batch feed
Continuous feed disposals run as long as the switch is flipped, so you can funnel food into the disposal while it's still on. These are the most common types in homes. 
Batch feed disposals only turn on when you put the disposal cover in place, so you run the disposal one batch at a time.
If you want a quiet garbage disposal with a warranty, you will have to pay extra. Units made of stainless steel parts last longer and will not become corroded after a few years helping you avoid repairs in the future.
Anti-Jamming capabilities are very useful to prevent food clogs and keep you from climbing under the sink to use the jam wrench to physically crank the teeth inside the disposer to free it.
Look for a unit that comes with all of the necessary hardware for installation such as the drain elbow and gasket.
If you are on a septic system, you must buy one that is septic tank compatible.
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Before You Begin
- Garbage disposal
- Electrical cord
- Plumbers putty
- Silicone caulk
- Water-pump pliers
Installing a Garbage Disposal
Most units come with the cord already attached. However, if you come across one that is not, you will have to attach the cord to the unit. Always follow the manufacturer’s instructions but the basic steps are to remove the cover plate on the bottom of the unit, and look for white and black wires. Then connect white wires to white wires and black wires to black wires using a wire nut. Then wrap black electrician’s tape around the nut to secure it in place.
You connect the green wire to the disposal’s ground screw. Those are the colors for most units, however, if you encounter different ones, read the manufacturer’s instructions provided.
Locate the drain flange and create a rope of plumber’s putty and press it on the underside of the flange. Insert the flange into the drain hole and press down evenly.
Note: If you have marble or composite sink, use silicone caulk instead of plumber’s putty to seal the flange.
Go below the sink inside the cabinet and install the back ring, fiber gasket and mounting ring.
Tighten the mounting screws for the upper mounting ring from below the sink. Alternate tightening each screw to pull the ring up against the sink.
Place the disposer into the mounting ring. The unit is heavy so this can be a difficult task. Try using a base of boards or a toolbox to set the unit on before you raise it so you do not have that far to lift. Make sure the outlet of the disposer is facing the drainpipe connection. Turn the lower ring clockwise until the disposer is supported by the mounting assembly.
Now measure the discharge pipe to length using a hacksaw. Install the discharge pipe to the outlet of the disposer and attach to the drain line with the slip nuts.
Connect the disposer to your dishwasher discharge line using hose clamps. If local code requires an air gap between the dishwasher and the disposer, mount the air gap in the countertop or an extra hole in the sink using a 5/8 inch drain hose to the ½ inch leg of the air gap with a hose clamp. Attach a 7/8 inch hose to the ¾ inch leg of the air gap. Make sure there are no low spots or kinks in the hose.
Finally, insert a screwdriver into the mounting lug on the lower mounting ring and turn clockwise until the disposer is locked into place. Tighten all slip nuts using water-pump pliers.
Turn on the water in the sink above and look for leaks below using a flash light. Plug the unit into an outlet, then flip the switch to turn it on. Check for any leaks while the water runs.
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Installing a garbage disposal can either be simple or more involved mostly determined by whether you have an electrical outlet under the cabinet already installed, and a working switch to that outlet above the counter.
Most new homes are pre-wired for disposals, but if you have an older home, this could cause the project to drag out a bit, especially if you have to call an electrician to put in a new outlet/switch combo. At that point, you might want to get a price on installing the entire unit and save yourself the hassle with the whole things.
If that is not an issue for you, then the process is straightforward and the basic plumbing skills involved should take less than an hour, even for a novice.