New Master Cylinder install issues

[bob_o]

I searched for answers already with no luck, but here's what's up. I installed a new MC and front soft lines on my non-power assist '75 GMC half ton (disc up front, drums in the back, stock system). After that was done, I proceeded to bleed the system using a small hand vacuum pump. There doesn't seem to be any fluid (or air) moving out of the bleeder valves at the wheels. I seem to remember reading somewhere that there is a release button (or something to that effect) on the proportioning valve? There is a little rubber boot covering something on the driver side of the PV, when when pressed, there doesn't feel to be anything underneath it.

Please advise, I'm running out of daylight and I have to drive this thing to work in the morning! Any help would be greatly appreciated.