Ok, so noob film question. I've got a couple of these compressable bottles to keep my developer and fixer mixes in, but no matter what I do I can't keep them 100% airtight. It's been around six months since I developed my last roll of film, and air has slowly crept into both bottles, are the contents of these bottles still good, or do I need to mix up some fresh batches?

And any ideas on how to keep the bottles actually airtight going out? I've tried running the lids under hot water before screwing them on, which is recommended by the manufacturer, also tried using some plumbers tape around the threads, but both bottles still decompress and let a little air in over time.