AG photographic sell 1L screw cap plastic jerry cans...I got 5 of them, for about GBP 1 each. I mix the XTOL using battery water (which itself comes in a 5L jerry can, so you could potentially store it in there if making more than 5l), in a big black bucket so I can see the stubborn crystals which take longer to dissolve. Once all clear, I divide it up in the jerry cans, using a funnel, filling the cans right to the brim. You could use marbles to get all the air out. I think my son would complain. I've never had XTOL expire on me, but I probably shoot 50 rolls of film a year. I use the XTOL 1:1, so it makes about 30 rolls of 35mm. Given its only about GBP 5 a bag, you may as well chuck it if you are concerned its expired and order another lot.