Tank Question

Hello all! I have been airgunning for a few years now, and I am almost ready to stick my toe into the PCP realm of things. I have a very limited budget (3 kids in private school will do that), but I acquired through work this week, for free, a fairly large oxygen tank, which seems to have been used for medical purposes. It was fitted with an adjustable regulator with a max output of 15psi, but the the bottle pressure was rated to at least 3000psi. It even came with a handy stand to keep the bottle upright. My question is, can this bottle be used for compressed air, if fitted with the appropriate regulator, fittings,etc., or am I better off attempting to trade it in at the local filling station, or just buying a different tank? As I said, I am on a budget, and I pride myself in reusing/recycling when feasible. Thanks in advance.
 
I do not see why not, as long as you do not use oxygen in it. May want to paint it to some other color. And of course observe all the inspection and safe handling requirements that are specific to that type of tank and pressure vessels in general. Getting it filled may be another issue. If the tank does not meet whatever standards are required for filling (proof of inspection, tank cannot be modified, etc) you may only be able to fill it yourself. Maybe better off getting a used SCBA tank with fill whip setup...can catch them once in a while under $380 on another major airgun forum. The first priority should be safety, even if saving money is the goal.