Here is a cut and paste of two posts I made to Photo Net in 2008.
(P.S.) I still am setting aside bottles of Xtol 2x stock and testing it to see if it is still good. I have never had a failure even with 3 year old 2x stock stored as described below.
Brian Quinn , Jul 27, 2008; 11:25 a.m.
I make Xtol up at 2x concentration and store it in 11oz. (330ml) Perrier water bottles. I tried to store in my darkroom fridge and it did crystallize but at room temperature it was fine (No Crystals). I open a bottle and dilute it 1:1 and that gives me 660ml of 1x developer for my tank. So I am always using developer from a full bottle. I have used bottles over 3 years after mixing it up and all is fine.
Brian Quinn , Jul 29, 2008; 10:38 a.m
One thing I forgot to point out in my earlier post is a key thing about long term storage of chemicals is to USE GLASS BOTTLES WITH METAL CAPS.
I little known fact is that plastic bottles will let oxygen in even if they are well capped. The oxygen will diffuse through the plastic (even a plastic cap) and oxidize the contents of the bottle. This is the reason that beer is sold in glass bottles with metal caps. Just a little oxidation of the beer ruins the taste. Beer that is sold in plastic bottles at sporting events has a very short shelf life. This is not usually a problem at a game as all the beer goes away very fast.