The whole system should be vacuumed down prior to extraction. You're solvent tank should've been vaccumed as well before filling it as atmosphere and water will ruin you're hydrocarbons, causing it to gel up. If you are using canned gas, it's more then likely a mixture of n-butane, isobutane, and propane. I would recommend recovering with dry ice for the reason that propane condenses at < -42F and isobutane condenses at < 10F. You would probably only be recovering the N-butane with an ice bath and that is only 40-60% of the volume. I wouldn't heat the collection vessel anymore than 85F. I personally recover around 60F. The reason for this is that terpenes and other compounds will boil out and collect in your recovery tank along with the gas. The dry ice pulls a vacuum on the system causing the compounds to boil at lower temperatures. If you aren't using one already, look into installing a molecular sieve or a drier filter or two to the recovery line. This will prevent any water from being recovered that has been pulled from the material and filtering out the other compounds that may have boiled off as well. Also, make sure you distill the gas 2-5X to remove any mystery oils that have been left over in the cans or tanks from the manufacturer. You can distill by using the cls without the column and just transferring the liquid into your cold trap (collection pot) and recovering it.