How unscrew a compression fitting (i'm not kidding)?
I've been doing some test fitting of my first custom loop and i've found that i can screw the compression fitting collar by hand and have it nice and flush to the bottom part. The trouble is any attempt to unscrew the collar just results in unscrewing the whole fitting from the radiator/block/whatever. If both ends of the tube are connected it makes it impossible to remove without cutting the tube.
My only thought is to use a couple heavy duty pliers but i'm worried about this damaging the fitting.
Needle nose pliers to hold the bottom, even that becomes tricky working inside the case. A barb with a worm-drive hose clamp will solve all your problems but if you want it to look nice you'll have to struggle a bit