Trouble bleeding rear brakes

[Mystic ZR-1]

Using the Mighty Vac backwards, as a pump. With flex hose disconnected
from the caliper.
Back fill thru the the bleed screw to ensure the caliper
is full. Reconnect hose and bleed normally after you're happy that the
caliper is full. You'll have to put the stock bleed screws back in to do this
as the Speed Bleeders have a check valve that may not let you do this.
FWIW: a friend once bought new calipers for his C3 and the holes for the
bleed screws weren't drilled thru...