the ASA (air source adaptor) can typically be swapped out for a aftermarket one, there are a few markers out there that the ASA is also the regulator for the marker and these can not be changed out typically
the ASA (air source adapter)
you screw the adapter into the gun, and then the co2 cartridge.
the ASA or Air Source Adapter is the part that connects the Co2/CPA tank to the gun, usually via macroline, and is usually found on the bottom of the grip. an on/off ASA is one that can be turned on and off, to make changing tanks easier.
Fifty caliber, but it is more of a toy than a paintball gun.
Disassemble the gun, and replace the back cap with the stock or take it to a paintball store, and ask them to.
It depends on the gun, but "both" is an acceptable answer.
The o-rings are damaged and are not making a perfect seal. Find which ones are leaking, and replace them.
replace the seals
You need an adapter (shown in link) then fill like a normal fill station.
The fluid, high pressure co2 (or HPA) is let into the gun when the tank is screwed into the Air Source Adapter, it is then stored in the valve, until the valve is opened, then it pushes the paintball out of the barrel when it expands. At the same time, it resets the springs and mechanical components (specifics depend on the gun model) , as the valve shuts and the gun gets ready to fire again.
On a paintball gun C02, or High pressure air is necessary. It is compressed air that, when the trigger is pulled and the marker fires, propels the paintball out of the barrel.
The sizes 9 oz and all the way up to 20 oz can be used for paintball gun. Some of the paintball guns are supposed to be used by the larger tanks. So the size of tank depends on your paintball gun.