Clean your hydration bladder with hot, soapy water, rinsing it with hot water.  For a more thorough cleaning, add ¼ cup of baking soda to ¾ cup of water and shake.  Add ¼ cup lemon juice and shake some more.  Vent the bag by loosening the cap away from your face.  Alternate shaking and venting a few times.  Allow it to dry with the cap off and propped open.  A thorough cleaning is necessary after filling your hydration bladder with beverages other than water.  If you do not give it a thorough cleaning, bacteria will build up in the reservoir and/or in the tubes.  A hydration bladder can be disinfected by mixing one ounce of unscented household bleach with one liter of clean water and leaving it over night.  In the morning, thoroughly rinse the hydration bladder and let it air dry.  You can freeze a hydration bladder by laying it half-full on it side in the freezer.