The 'release valve' is the knob on the end that connects to the tank.

Option 1: you buy a 'paintball remote line' which comes with the line, quick connect end, and release valve on the other end

Option 2: you buy just the 'release valve' and fit it to some tubing on your own. When I was at the paintball store they said it was 20 bucks or so for the remote line and 17 for the release valve alone. It seemed worth it to me to have the whole thing assembled and outfitted to control the kind of pressure the tank puts out.