This one drove me crazy before I figured it out. If the bleeder is at the bottom, push the piston as far back in the caliper as it will go. Remove the right caliper first. I used a very large C-clamp to hold the piston in place and then bled it holding the valve higher than the hose. Remove clamp and re-install caliper. Repeat with the left side. The first pedal push went all the way to the floor and the master cylinder needed to be topped off before completing the left side bleed.
