I don't recall ever seeing an amount or a unit. Only that it was refilled.
Unit could be a liter or a gallon. 2 liters would be very little. 2 gals could be possible. How do you know if they even filled it up all the way?:dunno:
I see on the internet where units are sold in 2.5 gal jugs, so two units would be about 5 gals. Full is about 6 gals, so that would be about right.