Both rear brakes not bleeding
 

This car did sit for probably 6 months before I bought it due to engine going bad. I was helping someone move and they noticed my rear discs we completely rusted over. They pretty much looked as if the pads haven't touched the disks. I took the rear brakes apart, cleaned everything and was going to replace the pads when I noticed the pads were all perfectly fine. I read this thread https://www.gmforum.com/showthread.p...r+Brakes+bleed and it is similar to my situation but its both rears that don't work and both fronts are doing all the braking. I hope it isn't a master cylinder, but after reading it may be. I am looking to see what I can do to check this before thinking about replacing it. Once pedal is pressed initially and the valves are opened, the brake pedal does not sink to the floor pushing fluid out. There was some fluid in calipers when I took the lines off and cleaned the calipers and VERY little fluid would come out of the rear flexible section of the line connecting from the metal line to the caliper. I had to twist the line around to get any fluid to drip out and gravity bleeding didn't work. If there was air in the line, it should push out with depressing the pedal and the pedal does not depress after opening valve. Sorry I am being redundant, but I am just trying to cover everything.
Any ideas?

It sounds as if the lines are clogged up in all honesty. The linked issue (thank you by the way) describes what happens when one channel of the master cylinder goes out. You should get fluid spraying everywhere when the brake pedal is depressed, and the lines are loose. Lack there of indicates blockage. I would be inclined to check near the proportioning valves, and other brake lines as well.

Yea I was going to check up on master cylinder but I read about bench leaking it or needing to take it in and I would rather be able to do this myself. Lines being blocked i thought about and in that situation that will suck replacing all of them running to the rear.

To confirm theories, you can start having an assistant depress the brake pedal, and you start cracking lines loose until you locate the blockage. From the master cylinder, on down. It would probably be wise however to just simply replace them in your case, not only will it likely resolve the issue at hand, but, living in the salt belt, will be something you won't have to worry about for a while. Next move is yours.

When I used to service Renault vehicles to bleed the rear brakes I had to disconnect the brake proportioning linkage because it would block all fluid to the rear if the suspension was hanging.
Were the front discs rusty as well?, if not you probably have a blockage problem.