I checked the drain line where it enters the sink drain and found no blockage. I haven't removed the dishwasher from under the counter to check the other end.
**Are you able to tell if the unit is just not draining or the dirty drain water is re-entering the tub?**
I'm not sure I understand the difference. I thought it mixes clean water and soap, sprays the dishes, then sprays with clean water, then empties the dishwasher. I run the cycle and am left with dirty dishes and dirty water in the dishwasher. I close the door run it again, same thing. Same amount of water remains. Forgive the ignorance...
I'll probably start with the piston since it could use replacing anyway.