Water does not drain completely. Therefore try removing the drain air gap. No difference. Moveover now, I have to change the drain air tube. How to I remove the tube from the washer?
First of all, is the machine draining at all? Can you see that the level drops in the machine or does it stay the same after hitting a cancel and drain cycle?
Often times you will find something caught in the drain valve like a toothpick, a bone, pit or other debris.
I would suggest you connect a separate hose to the outlet of the drain to a 3 gal or more container and then run a cancel drain cycle. If the water comes shooting out, then you can eliminate the machine itself and work on the line going to the airgap and then on to the drain itself. The rubber hose to it may have become kinked or filled with lime scale and clogged.
If the machine doesn't shoot out that water but the drain valve is opening (there is a lever on it that you can see moving and can even be pulled open by hand) then there is probably something caught in it. In rare instances, the drain impeller becomes so worn out that it no longer pumps with the proper volume to empty the machine. If that is the case, you will need to purchase and install a new shaft seal kit which includes the stationary seal and the larger vaned drain impeller. If this is not available thru Whirlpool/Kitchenaid, then you will have to purchase it directly from Hobart as they still use the same seal kit on their SR24 dishwashers.
The HOBART part number is 435102 and is available at any Hobart office. Just ask for the part number and do not tell them it is for a Kitchenaid machine. Most parts personnel nowadays at Hobart have little or no idea that we even owned Kitchenaid at one point in the past!