[rotorwrench]

If fluid flows out during the bleeding process, it should push the air out as well, at least till it's bled. If it's pushing fluid but won't build pressure then there may be a problem with the master or any one of the wheel cylinders or brake mechanisms. A bad flex hose can balloon during brake action but they will generally fail before that happens. Wheel cylinders with a problem should be gushing fluid out unless there is too much shoe clearance with the drums.

Some folks use a pressure bleeder to force fluid back to the master reservoir. If it's completely purged of air and still won't build pressure then there would be a bad rubber cup in there or something that it bypassing fluid.