[Tx Firefighter]

If it's not leaking out somewhere underneath the truck, the master cylinder is bad and allowing the fluid to escape out the back. It will either run down the firewall or into the booster, depending on if you have power brakes or manual.

Drum brakes bleed just like disc brakes. There is a small bleeder nipple on the backplate of each brake. Usually a small wrench like a 5/16 fits it.