Question:
I understand that you can use a CO2 fire extinguisher as a portable fill station with some kind of special coupler. Seeing as though the closest commercial field is two hours away, and that we play almost exclusively on our own properties, this would come in real handy for in the field fill-ups. Where can I find one of these couplers? Where can they be found for cheap? Can I build my own with simple parts found at any welding/scuba shop that carries tank/hose fittings? Seeing as though my local fire safety shop will re-fill a 5 lb CO2 tank for $8 which would equate to 140 oz. of CO2. or (7) 20oz fills. Which would be much better than what the local pb shop charges for fill-ups: 9oz = $2 12oz= $3 16oz= $4 20oz= $5 Where can I get the necessary "re-fill coupler" for cheap?

Answer: I understand why you want to do this, but when someone has to ask even the most basic questions about this sort of thing, it makes me nervous. You need to do way more research, not only about fittings, but about how CO2 behaves and how it is handled safely. I've seen a CO2 fill station such as you want fail with astonishing power, blasting a brass and stainless-steel fitting through a plywood wall, I've seen someone knocked off their feet by a CO2 fill station that got out of control, I've seen people literally freeze the skin off their hands because they didn't know what they were doing. This is not like pouring a glass of water, that CO2 is under many hundreds of pounds per square inch of pressure and it is always looking for a way out, one mistake and it can let you know with enormous force just how dangerous it can be. Please, be very careful, at least find someone who can go through the steps of using a fill station over and over until you can do it safely, don't just wing it and hope for the best.