It's always tough if you play on your own field with your friends, because once you run out of air, you're stuck. Not any longer!
Any Scuba/Dive shop will allow you to purchase a compressed air tank (typically, they stand about mid-thigh high and hold up to 3000psi). Once you've purchased the scuba tank and filled it, all you need to do is mount this fill station adapter to the top of it.
It's self-explanatory to mount, it can only go on one way. Attach your compressed air paintball tank to the fill nipple, close the release valve on the fill station, open the flow of gas using the large knob on the scuba tank, and air will flow into your paintball gun's compressed air tank. Once the flow of gas has stopped (meaning pressure has equalized between the two tanks), turn off the flow of gas using the large knob on the scuba tank.
Twist the release valve on the fill station, unhook your compressed air tank, and go play paintball! Simple enough. Depending on the size of tanks you're filling, a large scuba tank will fill up to 30 paintball tanks (or even more!) A perfect investment for you and your paintball friends who have your own field or forest.