I've been using rolston cheapo circlip pliers, with the smaller pins snapped off. The bent or side pliers is the one. Its all about applying downward pressure, at least to begin with as the mount is copper/copper coated so theres usually a bit of stiction.
I find the side shape allows me to press down with the heel of the hand and turn using both. Once its moving you can let off a bit of pressure, but they do still have a tendency to slip, so be aware and if you feel the pliers start to slip, take it off and reposition.
Best done with the caliper split and held firm. I use a vice and use protected jaws along with a couple of bits of wood shaped to better hold it (The joys of a small bandsaw
)
I could never tell if it was fully unscrewed as you dont get that little click so i keep turning it till i think it must ffs be off now
Then you can blow it out using a floor pump, and covering the little hole.
For this i use a bleed nipple, and remember to have it unscrewed a little. I didn't first time
using the presta side.
Because this is an incredible fiddle, and you need one hand to hold a cover on the little through hole, plus hold the pump to the nipple, it doesn't stay on itself, you need to hold it, and obviously hold a cloth over the caliper so the piston doesn't pop out and get damaged falling and striking something sharp that seemed to be placed there just for a delicate piston to impact with....
So hold cloth onto caliper half in one hand, using thumb and small bit of plastic(cut from a butter packet) to cover the hole(leave the tiny o ring in place, acts as a better seal) The pump held firmly against the bleed nipple that is screwed out slightly...otherwise....
Then with the pump extended and handle between your legs, sit down on it.
You may need to rise and sit a number of times to get thee pressure to act, so best done in private because it must be rather comical looking.
For the more dexterous amongst you, the pump on to the nipple, the protective cloth, holding the caliper and covering the hole, can actually be done on one hand. Leaving the other free to operate the pump handle.
Or have a friend help, or use a compressor