bungie
A correctly installed dishwasher waste sits tight up under the sink top. this is to stop the backflow.
Usually the air gap is built into the system, ie the air contained in the garbage unit, or when connected to a trap it is the break between where the dishwasher hose enters the trap and the water seal of the same trap.
Extend your waste pipe from the dishwasher to reach up under the sink top and back down to your garbage connection, and remove what ever you used to make your own air trap.
This way when it starts to block it will fill the sink first, given you a chance to see it before it floods you cupboard. plus it also gives it a head of water to help suck it down the line.
