■ Air Gap For Dishwasher
All dishwasher drains need a air gap before connecting to the garbage disposal.
This air gap prevents back flowing the sewage to the dishwasher.
Actual picture of the air gap connection from the dishwasher to the garbage disposal (bottom view of the counter top)
  ■ Dishwasher Backs Up
If dishwasher drain is clogged, soapy water willcome out to the front door.
Dishwasher drain means the pipe line between the dishwasher and the air gap.
Most of dishwasher drain is small and corrugated so it is easy to be clogged by the small food debris.