I have a 22 cu foot Aerox O2 tank. I also have access to the H tanks with medical oxygen at the veterinary clinic I sold a few years ago. I am considering asking the new owner if I could refill my portable from his H tank if I purchase an adapter, (and pay him an appropriate amount) but I'm not sure how good of an idea this would be. Is it dangerous? Is there anything I need to be particularly cautious about? Are there variations in which adapter I might need? Would I need to use a full (or nearly full) H tank to assure adequate pressure?