I almost always use 3/8" covers for walls and 1/2" for ceilings. As for the 3/4" we only use it for old rough walls or stucco. By the way, we never wash roller covers. It takes so much time to get them really clean and once washed the finish is not as good as using a new roller.
If I had to clean covers with a water hose I'd chunk em to...
I found this really cheap gizmo many years ago, fits a standard water faucet, forces water through a slot inside the ring so paint can't run from it,..insert the cover through it ( as many times as necessary). Cleans up to 3/4" naps.
I have one of these attached to a faucet over my deep well shop sink, you can clean ALL the paint from a cover in about a minute or so ...
rmichael