For long time storage of mixed x-tol I've bought two "brown/orange" opaque normal plastic bottles, and then I have planned to use one of the accordion bottles I have for "working mix" and refill it when empty from the normal plastic bottles (2 liters at a time). Right now it's just a bit less than 1 liter in the accordion and 2x2+ liters in the normal opaque bottles. I am sure this will be just fine. My second accordion is filled to the brim with 1+31 Studional.