Why is my dishwasher draining out of the drain air gap?

The rubber hose leading from your airgap to your garbage disposal or drain pipe is propably plugged. Remove hose and clean or replace. Also, when you remove the hose leading from the airgap to the garbage disposal, check to ensure that your stopper plug is removed from the garbage disposal.

The stopper plug is a metal or rubber plug placed in the garbage disposal for people that don't have a dishwasher. The best way to remove this plug is by taking a screwdriver and placing it on the plug and gently tapping the butt of the screwdriver with a hammer until the plug pops out. Use metal fingers to remove the plug from the upper hopper chamber of the garbage disposal or (if you are daring enough) remove with your hands.