Brake bleeding issues

New late model aluminum master, blench bled before installing
New front brake lines
New disc/drum distribution block
New 73+ calipers
Original line to rear
Rear drums

When the pedal is pumped, no pressure gets to the rear brakes. At the same time, the rear bowl of the master (going into the top port on the distribution block) gets pressurized and shoots out a fountain of brake fluid when opened after pumping the brakes.

Any ideas?