Recently I opened my e-mail box and found a note from a professional photographer in the Netherlands, Frank Viergever. He had one of those wonderfully simple ideas that make you wonder why no-one's thought of them before.
Frank's idea is to use Vacuvin stoppers that are sold for sealing partly used bottles of wine, to seal bottles of working strength developer. The Vacuvin stoppers are used with a special hand-operated pump that extracts air from the bottle of wine to stop it deteriorating. He said that he's been using it for several years now and that his developers keep really well.
You need to store your developer in a narrow-necked bottle that will take the stopper as a tight fit. We tried Paterson and Ilford and found both of these were too wide, but all Agfa bottles - from the very small concentrated Rodinal to the one litre packs - have a mouth exactly the same size as a wine bottle, so the Vacuvin works perfectly. Be careful the developer is not up to the top or you can pump splashes of it out along with the air.
I've used Vacuvin stoppers for their intended purpose (if I can resist drinking the rest of the bottle!) but it hadn't occurred to me to use them for developers. Many thanks for the idea, Frank. You can buy a Vacuvin pump and two stoppers for about �8 (GB pounds) at hardware stores, supermarkets and wine merchants.