Replacing an existing disposer with one of the same size is simply a matter of disconnecting and reconnecting fittings. However, if there is no existing disposer or if the new unit is a different size, you will need to reconfigure your sink trap.
A disposer must be plugged into a GFCI receptacle or directly wired to a junction box that is controlled by a switch. The switch is typically on the wall above the countertop. If the proper wiring is not in place under your sink, have an electrician do this work for you.
Local codes may regulate the use of disposers. Codes may require that a dishwasher drain hose be routed through an air gap before entering a disposer.
Installation, parts, and procedures vary considerably among disposer models. Follow the manufacturer's directions.
One to three hours, depending on changes to plumbing
Screwdriver, wire strippers, groove-joint pliers
Making simple electrical splices, installing a basket strainer
Remove an existing disposer or part of the trap, and the strainer
Garbage disposer, cable clamps, appliance cord (thicker than normal extension cord) or armored cable ("whip"), wire nuts, plumber's putty, trap parts
Remove the electrical cover plate from the bottom of the disposer. Install a cable clamp and run an appliance cord through it. Strip the wire ends and splice the wires -- black to black, white to white, ground (green) to ground. Cap each splice with a wire nut. Replace the cover plate.
To install this type of mounting ring, slip on the fiber gasket and hand-tighten the support ring. Slide the mounting ring over the flange and install the cushion mount, making sure the groove on the inside fits over the lip of the sink flange. Scrape out any excess putty on the inside of the sink.