How much IPA should be available in the tank?

For a normal extraction in the standard 25-40 grams herb tube, you will need a minimum of 360ml IPA available in the tank.
The smaller 10-20 grams herb tube will need a slightly less amount of available IPA pr extraction, but if you have min. 360 ml available in the tank, you are on the safe side.
Most of the IPA is reclaimed in the closed-loop system, but you will lose 40-120 ml IPA pr extraction as residue in the wet herbs.