[LazyPup]

The code requires that a dishwasher must discharge through an indirect waste system. Discharging the waste into the dishwasher port of a garbage disposal is an approved indirect waste method and therefore the air gap may not be required, however, some local codes demand an air gap on all dishwasher drain lines.

If you have a dishwasher but do not have a garbage disposal you are required to have an air gap in all cases.

Also, if you have a garbage disposal, the dishwasher is required to be connected to the dishwasher port, and may not be connected to a drain line downstream of a disposal.