I have about eight years of experience with using Xtol in replenished fashion.
The working solution was stored in a 2 liter brown plastic chemical storage bottle, which never failed me once.
The replenisher, which is nothing but pure stock Xtol developer, was stored in a container just like the working solution, and one accordion bottle, so that I could easily get rid of excess air in the bottle. When the accordion bottle is empty, I fill it back up with what's in the other 2 liter storage bottle.
In my eight years of using Xtol, the accordion bottle has not failed me once, even when I stored stock developer in it for as long as 10 months during a creativity block period. The activity was the same. I use local tap water to mix my chemicals.
Bottles were always stored in the basement, completely away from any sunlight, and in temperatures between 50 and 75 degrees Fahrenheit.
Xtol is an amazingly robust developer, and does not deserve the evil rumors that are spread about it.
I should say that I have also used Edwal 12 and Harvey's Panthermic 777 in exactly the same way as Xtol above, using standard and accordion brown plastic bottles. Never a problem. Activity always perfect. Make of it what you will.