time to drop some knowledge....
pretty much guaranteed it has a pressure release. it should be right next to the floor valve and looks kinda similar, just can't stick a pump in it cause it's one way(going out). x2 on checking the prv tho. they get a little bit of shit in em and don't work right and before you know it you blow an i beam in the floor. they make special wrenches to pop em out. worth the $10 investment vs blowing the floor(+ the same wrench takes the rest of the valves out if you ever need to). nrs's website sells em.
tear aid type A patches (type B only works for vinyl, A is for everything else) will hold for a small leak on flat water, but you gotta put a solid patch on it before you use it much.
clean the whole area real well, both patch and boat, with alcohol. if it's not clean the patch won't hold for shit.
get a heat gun, or even use a hot ass blowdryer. when you layer your glue on both the patch and the boat, let the last layer of glue dry then heat it up with the gun to re-activate the glue, then stick it on. then more heat while you press the patch down firm. i use a trailer hitch ball, it works great to press that fucker down tight.
use stay-bond glue. it works great on just about all boats, and definately is the best glue for an otter boat. it's a 2 part glue. mix in just a little of the activator, it should be about the color of coors light.
if you have any other/more specific questions on patching this thing just lemme know. unfortunately i have a lot of experience patching up rubber!!
...either way finding a boat like this in the trash sounds a better dumpster score than i've ever heard of!! congrats man and enjoy!!
All I need are some tasty waves, a cool buzz, and I'm fine. - Spicoli