I looked into this but have not done it. To get liquid CO2 from the bottom of the larger tank, rather than CO2 gas from the top, you need a siphon tube in the 20 lb, or larger, tank , a CO2 fill station with the correct fitting for your tanks, and a scale. The smaller tank is filled by weight. The tare weight (TW) is stamped on the neck of the tank - that’s the empty weight of the tank and its valve. You fill to that plus the CO2 weight. For example, my 5lb aluminum tank has a TW of 7.7 lbs, so full it is 12.7 lbs.
I go to my local welding supply shop. I got a new 5lb cannister with my kegerator. Fills cost me $18 and last roughly 6 months.
Rad
