does this have AC?
there is a valve in the hose, just before the hose goes through the firewall. this valve controls the water to the heater core inside the truck. find that valve, and give it a smack. you probably should do the mentioned cutting of hoses, and flushing the heater core.
Anti freeze is TOXIC to animals. if you are goign to get into the job ensure you dont pollute the environment, and dont harm animals. antifreeze actually smells sweet to animals so they drink it. be careful