Cannot fully drain essence from Hugo's tank

[PetiteOmega]

I've tried what feels like everything to the point of becoming severely frustrated. I can drain two thirds just fine and am left with two empty jars and a full shadow tank, but no matter where I place an empty jar, I cannot get the option to drain the last third. It sadly means I cannot move on with the game, as it's the only part I am missing.

How did you guys solve this? What am I missing?

[shvenda_s]

must first empty all the essence from the shadow tank.