I have never been able to successfully bench bleed a master. As you state, it's messy, annoying and I always fight air in it regardless. I've tried the looped hose method as well as the method where you simply depress the piston and plug the outputs.
Perhaps my technique isn't correct, that's certainly a possibility.
What I do now when I need to bleed a master is reverse bleed. I purchased the cheapest reverse bleeder I could find to try it out and it gave me a great pedal right away. The idea behind them is that air naturally wants to travel upward, so why fight that? I started with just enough fluid in the master to make sure the valves were completely covered. Then, starting from the farthest caliper and working towards the nearest, reverse bled through the calipers, up the lines and into the master.
Because I can't leave well enough alone, I've been through 3 master cylinders, 2 boosters and a complete set of calipers and rotors in the past 4 years and that little plastic part has saved me countless ours of bleed time and a whole bunch of wasted fluid.
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-Jason
1969 Pontiac Firebird
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