yes they are refillable
If you are asking about the small 12 gram C02 cartridges, then,"No" they are not reusable. However, larger tanks (like 20 oz) with pin valves on the top are refillable.
Call them and ask!
At a paintball or sporting goods store.
They need the small sealed CO2 cartridges, not the screw on tanks. but yes they need Co2 to function.
drain the tank, throw it away
There are non refillable, disposable cartridges that range from the standard 12 grams to 4 oz. There are also small refillable 45 butt stock tanks and other small and long tanks like it. After 4 oz, a tank must be fitted with a "burst disk" which allows it to bleed out if over pressurized. Any refillable tank over 2 inches in diameter needs to be hydro-tested every five years.
No, you must have it refilled at a paintball field or pro-shop. You cannot refill paintball tanks from low pressure Soda dispenser C02 tanks.
Paintball guns can use Co2 from any company, they are all built the same. You can find valved tanks and 12 gram's at sporting stores, paintball fields and proshops.
co2 tanks are fine for stocks. But if you want more they make caps for the end of the co2 tanks that have a thing like a stocks end. (opsgear.com has em) But as long as the stock outreaches the co2 its good
You must have them hydro-tested or throw them away. You will not be able to fill them legally.
Cheap co2 tanks are about $20. Carbon air tanks go all the way up to $125 or so