2nd Gen Non-Engine/Transmission brakes on a 95

[CRead]

My friend has a 95 that has some serious brake issues. From what I was told is he was having issues with the master cylinder. He replaced the master cylinder. And the first problem whatever that was was fixed. But now the brakes act like they have air in them. He has bleed the system many of times. He thought he got a bad master cylinder so replaced with new and bench bled this one. He said that if he pumps the brakes they start to work but looses all pressure if he does not pump. He adjusted the rear brakes all the way just to see if that was the problem. Still has same problem. Checked the whole system for a bad line. No bad lines. He said the fliud in the master goes down when he pumps it up but comes right back when he lets off. He talked to some brake places and they said to back bleed the system but no one can say how to do it. Does anyone no anything please let me know. Thanks. This is not mine this is a 95.