Poor snake...he's lucky to have survived. I wonder if he was without a water bowl previously....that would explain both his excessive thirst and his poor shed when
you got him. It's not normal for them to drink that much at one time...since his previous owner seemed clueless about his need for heat, he may also have thought
that snakes don't drink water. (Honestly, I've met people who think that! And they are so wrong!) This BP needs lots of rest & "TLC" to get healthy- make sure his
"hot hide" is the right temperature (not over 91*) as snakes don't always know when they are being harmed by excessive heat, & this one is trying to survive. Snakes
literally cannot digest or even move when it's too cold...their metabolism is dependent upon finding the right warmth in their surroundings. A hiss is just what it
sounds like: "leave me alone!" He was stressed & just defending himself...always nice when a snake warns you instead of just biting. Doesn't mean he'll stay cranky-
he's been thru an awful lot, that's what it sounds like to me. It may take another week or more before he feels like eating again...be patient. How is his breathing?
Any whistling sounds? crackling sounds? It's a miracle if he isn't sick...you might do well to have an experienced herp vet check him out since you are fairly new to
keeping snakes. There's only so much we can tell you (medically) online & without seeing the actual snake; we cannot substitute for a veterinarian.