I still say that collapsable bladders like those used for hiking/camping are the easiest and best solution. Many of my chemistry (I buy 5-15 gallons at a time) comes in these, which is where I got the idea. Also depending on your desires, those vacuum seal kitchen bags (used to be called seal-a-meals) work quite well. I never used mine at home so I hauled it to work and viola!, get use now. And as it gets used down you can just cut off the extra length and re-seal. Or throw away and start again. When they need darkness for storage, I simply put that bag/bladder in a black plastic overlay.