I apologize in advance if many of you already know this, but I thought that I would pass it along just in case it helps anyone. I develop primarily in Microdol, which requires mixing at a high temperature. I develop it 1:3, which usually leaves me with a fair amount of leftover. I always parse out the developer in empty plastic Coca Cola bottles because I assumed that they do not breath at all. I fill them ALL the way to the top and cap them tightly. This has worked very well and developer has lasted full in these for months. My only dilemma was what to do with a half empty bottle. Well two months ago I took a half empty bottle and simply squeezed the sides until the liquid level reached the very top and then capped it. It kept that squeezed form. I developed using that developer 2 months later and noticed no difference. I bit easier than marbles. Just another idea for you guys.