While the drain connection for a garbage disposal is nearly universal and fits standard sink drain holes of 3 1/2 to 4 inches, the size of the disposal unit itself is not. You must have enough space in the cabinet underneath your sink to accommodate the disposal's housing. A larger model may not fit in a compact cabinet or if the existing plumbing is arranged in an unusual way. Before buying a new garbage disposal, measure the available space under your sink. If you are replacing an old unit, it's often easiest to choose a new model of a similar size.

You may be able to install a garbage disposal on your own, especially if you're handy or have some experience with plumbing. However, if you have any concerns or want to make absolutely sure that the connections are installed correctly, you may be better off hiring a local garbage disposal installer to do the job. 

These appliances do unscrew, but you need to disconnect everything properly when you replace your garbage disposal. Make sure you shut the power off to the area first and check that it’s off with a voltage detector. Disconnect the main drain line and P-trap, and then disconnect the dishwasher drain line if you have one connected. You can then unscrew your garbage disposal using a disposal wrench. Just make sure you disconnect the electrical lines before removing your appliance.

Most garbage disposals have a reset button that can be triggered with a tool as simple and accessible as your index finger. That said, if you need to perform a more in-depth troubleshooting step, like manually moving the arms inside the unit or rotating the impeller plate, a hex wrench is the most common tool you’ll need. Most garbage disposals come with a hex wrench.