You want a welding tank...that's the type of fitting the Milwaukee regulator's designed to fit. You really just want a standard CO2
cylinder. I think the one's they have for fountain pop machines has a different fitting on it that won't work.
Your best bet is a fire extinguisher store, or a welding supply house. If you simply ask for a CO2
cylinder, you'll get the right thing.
It should be measured in pounds, since CO2
is sold by weight, not volume.
I'd check the welding place, and see if they rent tanks for a security deposit. That's what I did...$85 deposit, which I'll get back if I ever decide to stop the planted tank thing. A new tank was $110 here, but prices on weird stuff like that get inflated, espeically when there's 1 fire extinguisher store, and 1 welding supply house within a 60 mile radius.
The problem with buying a used tank, is that you don't know if its still safe, unless it still has it's last hydrostatic test sticker on it, and it's still valid. When you own a tank, every few years you have to have it tested, for about $25 and it takes a day or two. By leasing a tank, the actual owner worries about the hydrostatic testing, and you're ensured a safe tank (provided you got it via a reputable dealer).