Speedball, I was hoping you would provide me with some additional information on the air vent that's on the sink. I don't know if you are understanding me, or I am using the wrong terminology. Another plumbing expert, on another site, said water is not suppose to come up through the air vent. You say if it DOESN'T come up, the dishwasher is not working properly. My old dishwasher worked fine for years, before it started getting clogged. When it was clogged the water would backlog up through this vent. Now I have moved and the dishwasher here, is just "sometimes" having a little water come up through this vent. The dishwasher is getting the dishes clean, and the water is draining out of the appliance, somewhere. If I could draw you a picture, I would. The vent is located on the top of the sink, next to the hose for the sprayer.

Good morning Grets,

A dish washer air gap device has but one function, and that is to provide a interuption or air gap in the drainage hose so that when you run your disposal it won't drain back into your dishwasher. The fact that you only get a small amount of water through your air gap tells you that it's clogged and isn't functioning. The dirty water discharges up to the wye and then diverts directly into the disposal drain. To see how they hook up click on;
http://www.acmehowto.com/howto/appli...eck/airgap.php
We install dishwashers in all our new construction but not air gaps. We get the same effect by looping the discharge hose as high as we can in the cabinet and securing it with a pipe strap. Sincethe loop is higher then the disposal it drains into when the pump stops the loop fills with air and provides a gap to prevent dirty water from entering your dishwasher.
You said."Another plumbing expert, on another site, said water is not suppose to come up thru the air vent."
And did he explain this "air vents" function? What it vents? Anything? In all the dishwashers that I've installed throughout the years I have never came across a "airvent" for a dishwasher nor is one listed ever been in the parts lists.
I'll attach a picture of a typical installation so you can see what it looks like installed. The other plumbing expert was mistaken and if your air gap isn't working I would find out why.
My advice is to unhook the hose from the device and replace it with a continuous hose that you loop as high as it will go in the cabinet and secure it with a 1" pipe strap. That way you're sure. Good luck and if you need more explanation then this,
Air Gaps
An "air gap" is an anti-siphoning device that can be installed on the countertop to prevent the backflow of water in the sink pipes. It is installed in conjunction with dishwashers (and water softeners which are not addressed on our site). The drain hose from the dishwasher goes into the air gap and then into the drain. The air gap must be installed over the flood-rim of the receptacle --i.e. over the sink. If the sink actually did back up, the air gap would prevent "gray water" from going into your dishwasher.
Click on back. Regards, Tom