Dishwasher - water is out the air pipe

[George P.]

The tenant has informed me that the dishwasher (4-5 y.o. Kenmoore) has started pushing the water up the air pipe.
My initial reaction is the diahwasher's sewer pipe is clogged. But what else could it be?

There is a disposal that the sewer pipe is connected to (I think).

I am going there over the weekend to take a look and possibly fix.
Thanks in advance!

[Mitch Kronowit]

Eliminate the obvious. Are they running the garbage disposal before they run the dishwasher? If not, debris in the disposal could cause the air gaps drain hose to back up. Is the sink backing up? Check and see if the lines into and out of the air gap are clear as well. It could be the air gaps itself (cheap fix).

Good luck and report back what it was. Thanks.