[bobcowan]

Press on the pedal hard. Open the bleeder only 1/4 turn. Close the bleeder. Release the pedal.

If you open the bleeder too much, air can get in around the threads. If you open the bleeder when the system is not under pressure, air will enter.

Use a simple bleeder cup so that even with a little bit of back flow it will only backflow fluid, and not air.

If fluid is coming out the bleeder under pressure, then the MC is working. As long as the ports at the bottom of the reservoir are covered, there's no place for it to suck in air.

If the fluid out is roughly equal to the fluid in, there's not much of a leak.