I recently just had a 15 year old dishwasher replaced with a new GE dishwasher. I never had any air gap overflow issues with the old dishwasher. The previous installation was connected to an air gap, so the installer connected the new dishwasher in the same manner. I live in Chicago so i "think" an air gap is still required per code (or a high loop i'm sure). Regardless, during certain drain cycles on the dishwasher, the air gap will overflow water (about a cup or two) out the top of the air gap cap (without the decorative air gap cover on) and into the sink and counter. I say "certain" drain cycles because it doesn't happen every time...when it's a full drain cycle, the dishwasher pumps out thru the air gap just fine (pumps for like 15 seconds), but when it's a short duration drain cycle (where the dishwasher only pumps out for 3-4 seconds) then it overflows.

Other facts...
- the drain line from the dishwasher to the air gap was replaced new.
- there is nothing clogged in this new drain line and I connected some plastic tubing to the top of the air gap (without the cap on) and let it drain from the air gap into the sink to see if any debris was in there.
- I do have a garbage disposal, but drain line #2 (coming from the air gap) does not connect to the disposal inlet underneath the sink...it has it's own dedicated connection into the wall with a P trap.

is it possible that during a "short duration" pump out of the dishwasher, the water draining from the air gap into the drain line #2 doesn't have enough head pressure to "push along" the water already in the P trap, and thus backs up?

Also, should I just connect the air gap drain #2 line to the disposal inlet as most air gaps are connected? If I do that, how do I cap the previously used drain pipe once I remove the rubber hosing? I don't want to leave it open and create a drain vent underneath my sink!

any help would be great...thanks so much!