Drying a Hydration Pack Bladder

This is an old tip which I found in an MTB mag a few years ago, still it bears repeating. It's always difficult to get the bladder dry in the corners as it tends to stick together, the result being mildewy stuff in the corners which to be honest probably looks worse than it is. In any case there's no need to buy a dedicated dryer, just get a pack of 4-6 practice golf balls, the plastic ones with the holes, shove a few into the bladder and it's job done.