Here is a copy of my post elsewhere about bleeding brakes.
I think the problem lies in the rear cylinder design and arragement.
I know this has been discussed several times but here are some pic to illustrate the problem
This is the path the fluid takes when bleeding the rear cylinder.

There is only a small hole in the cylinder;

My solution is to fill the cylinder with brake fluid just prior to bleeding like this;

I hope thats not teaching my grandma to suck eggs, but I thought it might be usefull