I don't get the credit for this tip, because someone suggested it to me on a recent hike (John Christopher, I think). But I googled it and it sounds like a good idea:
http://sectionhiker.com/2008/09/10/ster ... efferdent/
Sterilizing Hydration Bladders with Efferdent
"This year, I’ve had a hard time preventing red mold from growing in my Platypus hydration bladders. I don’t know why mold started to be a problem this year, but I think I’ve finally found a way to clean it out of my bladders and prevent it from returning.
The secret is Efferdent, normally used as an anti-bacterial cleaner for dentures, but gentle enough for sterilizing the inside of platypus water bladders. To use, fill the hydration bladder up to about 2/3 of capacity and drop 1 Efferent tablet into the bladder for each Litre of water. After a bit, the tablets will start fizzing and turn the water in the bladders blue. The fizzing oxidizes any bacteria present in the bladder, killing and dissolving it. For maximum effect, tip the bladder over and make sure the blue solution touches all surfaces in the interior of the bladder. When the blue water turns clear in that classic Efferdent way, rinse the bladder out throughly with clean water, fold it up and recap until next use."
The only thing I would change about that is that I fill up the bladder completely...not sure why they say just 2/3 of the way. (?)
And another tip that many of us use is to store our hydration bladders and hoses in the freezer between uses....this doesn't kill bacteria but slows/stops the growth for that time.
