As a side note, I store 5L of Xtol using the same means as the box-o-wine.
The Fermtech "Wine on Tap" system consists of a sanitized oxygen barrier bag with a push-button dispensing spout and plastic shell that provides the "box" structure. The plastic shell and one bag costs about $23 and replacement bags are 3/$10.
After the Xtol is mixed, use a funnel to fill the bag and snap the push-button dispenser on. (Don't snap the dispenser on until the bag is full. It's meant to be disposed of with the used bag and nearly impossible to remove without damage.) Orient the dispenser on top and gently squeeze the bag while pushing the button to expel any air. There shouldn't be much. Then set it upright and you're good to go.
Dispensing into a graduated cylinder is easy with the push-button and the bag collapses around the remaining Xtol with no air pocket.
I have no trouble using 5L in six months, so I don't know how long Xtol will store this way. It should be good for quite a while, though.