Parafilm a friend to Film
This is one of greatest inventions of mankind. Parafilm is super stretchy plastic tape, which is used by chemists to seal bottles from air and moisture. Use this to wrap around neck of your developer/fixer bottles to seal them and make them less prone of getting bad. Only con is that after you peel it off, you must cut new piece of film to seal it again. It is almost impossible to reuse it. Although it`s cheap and you only need about couple of centimeters/ about one inch for each bottle. I suggest getting wider one, which is two pieces wide not the narrow one, as you need longer tape to wrap several times around bottle. Ebay is full of them, write either Parafilm or Parafilm M.
So a really good stuff to prevent film chemicals (Developer/Fixer) from getting old.
More info here: http://www.2spi.com/catalog/supp/parafilm.php