I just bought a 94 blazer silverado.
The breaks randomly stopped working, you have to pump them like 20 times to stop once. The break fluid is slowly leaking.

Anyone give me ideas of where to start diagnosing?

 

There's a Blazer 'Silverado'?

When the BRAKES quit working on your car, you look in the brake reservoir to see if there's fluid. If there's no fluid, you add some. If fluid still goes down you find the leak. It's wet and thin-oily.
If it doesnt go down in the reservoir, you change the Master Cylinder because the seals are old dried up and damaged.

 

Where the break fluid goes the hoses under it go to a seperate box where multiple break lines come out of. What is this called?

And the break fluid is leaking, I've filled it twice so far.

 

That would be your ABS system

 

I determined it was a leak in the passenger rear drum. I keep tried getting the drum off but no success. I figured the breaks are still engaged. I know there is a way to manually loosen them, can someone tell me how?