I haven't read all the replies, but in conversation with some fire fighters, they say the tanks cannot be refilled after the hydro runs out if they are being used for life or death situations (scuba diving, fire fighting, etc), but they feel they are still useful for other purposes, such as air rifles and putting air in tires. So, you might hit up a scuba dealer from that angle, or if you know a fire fighter, ask him if they will fill it for you. You might also ask him if they have an extra tank or two laying around they'd want to part with. I know several fire fighters in my area and have gotten an affirmative on a couple different places for some pretty decent air tanks.