I just got back from the appliance dealer and looked at both the refrigerator and dishwasher valves.
They both are checked to pressure!
Stepit, you were right ( I never doubted you
To purge the frig you would disconnect the 1/4 in line in the basement, apply a vacuum and both the ice maker and drinking water would be pulled from the frig.
The dishwasher would work the same way. Access should be under the sink? I have never used my dishwasher but I will make SURE there is no water in the dishwasher.
I hope this helps someone from flooding their beautiful camper.