One thing I learned from filling CO2 paintball cylinders, is if the cylinder is frosted over you get a lot more CO2 in the tank. The same applies for the little pounder propane tanks. I hook them up turn my 20lb tank upside down and open the value for a couple of seconds and then vent the lber with a nail, I use heavy gloves as the propane can and will freeze your skin. After venting, the cylinder is nice and frosty, then take a lot more propane that way, don't ask me why.
Works OK with CO2 with LP it vents when the tank is back to temperature.
