I store my XTOL in 250ml (topped off and tightly sealed) amber glass bottles. I use it 1:1 so I can't comment on used developers' keeping qualities, but, the unused developer has lasted as long as 5 months stored this way. I haven't had any problems in the last 2 years. The only problem I did have was when I stored my XTOL in one of those accordion type plastic bottles. It barely lasted 2 months.(posted 8399 days ago)