Andy,

Yes, you want to remove the fluid from the return side so that it is not so pressurized. You should be able to tell which is which because the pressure side will be a more hardy connection. I've never done the flushing by cranking the engine. I have done it by slacking or removing the belt and spinning the pully by hand. But, I was doing that on cars that did not have the single serpentine belts.

Charley