Xtol needs to mixed with water up to the recommended hot temp, around 90 deg F. Don`t do the room temp stuff.
Don`t store colder that 68 F/20 C. or you can get precepitation.
decent glass bottles with well sealing caps are an investment every darkroom needs. Sometimes plastic works, sometimes not. Some plastic have an air impermiable membrane. All this is hard to tell by looking.
Soda bottles need to be cleaned completely, not rinsed out.
The exp date is important on Xtol. If the bag is past date, toss it. Even if it all goes into solution and looks good, the shelf life after mixing will be a week or so. It was a bad experience that Kodak resolved by dating the bags. My bag was before they were dated. They replaced the Xtol, buy my photos are gone forever.
I now mix D76 a liter or two at a time. Always fresh, always works, cheap as dirt. T Max 100 and 400 are beautiful in D76. TMY-2 is shockingly good.