How a Garbage Disposer Works
The garbage disposer uses an spinning impeller blade to force debris into the blades along the side. As it spins, it grinds the debris through the blades into particles that can easily be flushed through the drain. The disposer relies on lots of water to turn the food bits into a slurry that can be easy flushed through the drain.
Before beginning work on the garbage disposer, unplug it or shut off the power at the fuse box or circuit breaker panel to avoid unexpected operation or an electrical shock hazard.
The garbage disposer is not good at grinding fibrous foods like banana peels, celery, artichokes and corn husks. Fibrous foods do not grind into particles so much as strings, which tend to jam the disposer and clog the drain.
The disposal is mounted directly under the sink. The water from the sink runs through it to the "P" trap. The "P" trap's purpose is to hold a plug of water between the sink and sewer line under your home. Without the plug of water, sewer gas could flow through the sewer line and into your home.
If you have a double sink, the second sink's drain usually bypasses the garbage disposal and connects directly to the drain line just before the "P" trap.
If you have a dishwasher, typically the drain line from the appliance connects to an upside-down "Y" connector. The "Y" connector connects to an air gap above the sink. The air gap is vital to prevent a suction from occurring which could draw sewage into the dishwasher. If siphoning occurs, air is pulled in through the air gap rather than water from the waste line.
Ordinarily water runs from the dishwasher to the "Y" connector and into the disposer above the blade so that debris from the dishwasher can be ground if necessary.