#4 I only use glass jars (mostly canning jars) to store leftovers. When I do end up with the science experiment I can boil my jars and lids to get out all the icky stuff. It is great since the glass always comes clean, no stains! If it is just too disgusting I can just pitch the lid because the lids and rings can be bought separately. The leftovers also last much longer in glass then plastic.