Here are the steps you will need to follow install a garbage disposal or replace an old one.

Step one:
Make sure that the power to the circuit that is serving the disposal is shut off before you begin any kind of work. If you are replacing the old disposal in addition to the power being off you also need to unplug the disposal or disconnect the wiring before your remove the unit. To ensure there is no charge use a voltage tester to test the bare ends of the wires.

Step two:
You will need to disconnect and remove the existing waste assembly, from the sink flange to the trap. When doing this make sure you have towels and a bucket nearby to catch any debris.

Step three:
Once the waste lines are out of the way, you will need to remove the mounting assembly from the disposal and install the new flange in the sinkhole. When installing the new flange you will need to apply a coil of plumber's putty around it before dropping the new flange into place.

Step four:
Attach the upper mounting assembly to the sink flange. When doing this place a heavy object, such as a thick phone book, on top of the flange to hold the flange in place. You will need to follow the manufacturer's directions for gasket placement. Once the gasket is placed, slip the mounting ring over the flange. Then slide the snap ring onto the flange until it pops into place in the groove on the flange.

Step five:
Tighten the three mountings crews until the assembly has a tight seal against the sink.

Step six:
Now you need to get ready to attach the disposal to the mounting assembly. To do this you will need to attach the discharge tube. Then inspect the P-trap and clean out any hardened waste. Next you will need to prepare the dishwasher drain connection, which is done by knocking out a drain plug from the dishwasher nipple and attaching the drain hose from the dishwasher.

Step seven:
Place the disposal under the mounting assembly so that the mounting tabs can slide over the mounting tracks. Lift the disposal, and insert the top into the mounting assembly. Next, rotate the lower mounting ring until all three tabs lock over the ridges in the mounting ring. Use the wrench that is provided or a screwdriver to tighten the ring.

Step eight:
Rotate the garbage disposal so that the discharge tube aligns with the drain trap. If your sink is a double-bowl model, you will need to replumb the waistline to attach the disposal. The easiest way to do this, if you are lucky, is to add an extension tube. If you are not lucky, you will need to replace the entire assembly.

Step nine:
Now you can disconnect the disposal to the power. You can either run yourself or have an electrician do it for you. You will also need to install a GFCI receptacle. If your disposal did not come with a plug on the end of the cord, you will need tow ire the recommended grounded electrical cord to the disposal. If it came with a plug, plug it into the receptacle.