People come up with some of the most ridiculous reasons to not use a certain product.
5L is too much? We're not talking 25gallons of solution.

2L Air-evac bottle, 8 US$ at freestyle.

1L Air-evac bottle, 7 US$ at freestyle.
They also sell 5L non-collapsibles for 3 US$.
There's really no issue here. 2+2+1 = 5. You might be able to find them cheaper, but 25$ is easily payed for in a year by the cheap cost of XTOL itself. Not to mention the containers are generally useful. Alternatively one can come up with various combinations of hard and collapsible containers such that atleast 1 is always the active and the others are 100% filled storage.