Undo the line at the MC and stick your finger over the outlet. Pump the lever to bleed the MC. Hook up the line. This may do the trick or you may need to undo the line lower and bleed the line with your finger over the outlet. The problem is there is so much volume of air that the MC can't get a strong pump to fill the system. Fluid dribbles down but the air wants to rise. Lightly tapping the MC to get little air bubbles coming out the reservoir holes is another trick. Once the system is filled then the brake fluid can be pumped through with enough authority that the air is passed out with the exiting fluid. It's sometimes a tough job. Some even resort to lifting the calipers above the MC to bleed. I hope this helps.
Tom Graham
