To add onto ol' grouch, sometimes I'll start by gravity bleeding the brake lines. Fill up the master cylinder with fluid, then open each of the bleeder screws one by one (starting with the one farthest away from the master cylinder to the least farthest away) until you see fluid dripping out of the bleeder screw without bubbles. Tighten the bleeder, then go to the next one. Once done gravity bleeding the brakes, go back one last time and use the two man bleeding process to bleed the brakes one last time on all 4 wheels. As long as there are no other leaks anywhere else in the brake system, you should end up with a rock hard brake pedal.

 

An experienced tech told me on GMT800s he vacuum bleeds and pumps the pedal. Says this negates any need for a scan tool to activate the ABS pump (not that that is in question here)

But, perhaps a technique for difficult bleeds....

I've never tried it so can't relay personal experience

 

I like using a MityVac tool to do vacuum bleeds sometimes, too. Still nothing beats a pressure bleed system by introducing low positive pressure at the master cylinder to push fluid through the brake lines to bleed the system.