What is a good way to dry water bladders for storage to prevent mildew?
With Camelbak’s I can fit my hand inside bladder to towel dry followed by some sunlight. You might have to wedge something inside to keep open for final UV dry. MSR Dromedary have too small opening for manual dry but can fit long tongs inside to swab with towel. Former wise poster from Australia, Gnarly Dog, just left his filled and frozen to retard undesired growth. Regardless of technique, mine get hot soapy water and bleach or baking soda every so often. The Camelbak hoses require removal of mouthpiece and get centrifugal treatment by holding one end and whirling around and then time in sunlight.
My big msr dromedaries I drain and leave open in the sun for an afternoon or two with the cap off. Store with the cap on.
My smaller hydration bladders I try to keep filled and occasionally put Aquamira in to keep from getting funky.
Rinse mine with a solution of vinegar and water then insert a balloon whisk in the bladder to keep it open while it dries in the sun.
A bottle brush with a long handle works also.
Sunlight to dry, store in freezer