I store the Unicolor 1-liter solutions in PET plastic bottles, squeezed to remove air before capping and placing them in the dark, and I filter them between each use.
Unicolor states that 25%, 50%, or more rolls than the capacity they indicate can be developed if the chemicals are used within a few days and can be used for a longer period as long as partially used solutions are used every day or two. My statement of using the chemicals in 2-3 days may be conservative but it's in line with Unicolors' advice and I take it that weeks or months of storage would probably not be good. Once I developed a 16th roll 2 weeks after developing 15 rolls over 3 days and it was noticeably thin, which corroborated Unicolor's advice.
But maybe this is only applicable to Unicolor, where the solutions are made from powders. I'm glad to hear others can get more time out of their working solutions.