All I know is I once poisoned myself by not cleaning out my flashflow bladder well enough. It was my running one- so a waistpack, and the bladder didn't come all the way out, so I guess I was bad about getting the gunk out. I went for a week getting ill after every run before I figured out that I was poisoning myself!
Now I'm diligent about it. I soak the entire thing in a bleach/water solution once a week and clean in out with soap and water in between .
Kind of a pain, but getting the revenge is worse!