CO2 Tank Power Filler III Transfill Tool Larger Tanks from Power Tank. The Power Fill-III CO2 Transfiller Tool is used to fill CO2 bottles from larger CO2 tanks. CGA-320 to CGA-320. Unless your Large tank has a siphon tube inside you will flip your Large tank upside down to get the gas to the valve.
Try to chill the smaller bottle to get a more complete fill. You will only be able to get three 5lb. fills from a 20 lb. tank.