USD caliper sir???
If so I'd suggest unbolting it from the mount - pushing the pads/pistons right into the caliper and then putting a suitiable block of wood or something between the pads.
Then try and get the caliper higher than the master cylinder - pump the pedal a few times, crack the bleed nipple (WITH CARE AS IT MIGHT SPURT!)
Repeat until hard......sorry, the brake NOT anything else
Cheers - Frank