I've never shared a Camelbak with another person, but I have cleaned the bladder a couple of times. I put a drop of chlorine bleach in a gallon of water and poured it into the bladder. It was allowed to sit for a few minutes, then was drained and rinsed and drained again. A wadded paper towel was inserted into the bladder to hold the sides apart. The bladder was then hung upside down (fill hole down) in the shower until dry before using again.
These things are now a military issue item. I wonder if they have a procedure for doing this.
There is a valve so no back-wash should occur...I think if you disinfected the mouth piece you would be ok...I flush mine with a vinegar solution and rinse it well periodically....seems to do the job....
Run hot water from the faucet. (Don't exceed the manufacturer's recommendations for temp or you'll melt the plastic - the bladder is the most vulnerable to this.)
Fill the bladder, then use the bladder brush to scrub out the inside.
Fill the bladder again, drop in one of the Camelbak cleaning tablets. It will fizz up.
Scrub the bladder until clean, rinse out, and fill with hot water again.
Put a few drops of hypochlorite bleach, brush out the inside again, then rinse the bladder.
Fill the bladder with cool water and rinse a couple more times, then hang to dry with the reservoir dryer provided in the cleaning kit.
Take the insulation jacket off of the tube so you can see if there is any contaminent or mold growth on the inside.
Run the tube brush through the tube from each end to scrub out the visible contaminents.
Run a small amount of hypochlorite bleach (Chlorox, or similar brand( through the tube, then brush it out again.
Wash, scrub, rinse, sanitize, and rinse the valve, cap, and bladder lid.
Let everything dry, then re-assemble with the spare drinking tube.
The drinking tubes get contaminiated much faster than the other parts of the Camelbak, which is why I alternate mine with the spare.
There are other methods listed here , but I'd stick with the complete dissasembly, wash, and bleach method I described, especially if sharing the Camelbak.
Periodically slide the tube insulation jacket back and see if there is any black or other discolored buildup in the tube. If so, you have either bacterial or mold contamination in the tube, and it's time to clean and disenfect, even for one-owner Camelbaks.
The problem with sharing a Camelbak is that you need to do the cleaning and disinfection every time you switch users. This procedure is time-consuming, it can be frustrating if the insulation jacket has gotten hot and shrink-wrapped the drinking tube, and you can ruin a uniform if you spill or spatter the bleach.
In the long run, it's much easier to just purchase a Camelbak for each individual who needs one.
I didn't, either, until I had got sick from contaminents in my Camelbak - twice.
The first time was ignorance - I didn't know to get a kit and clean my Camelbak and got a nasty GI bug at an all-day swiftwater rescue class.
The second time was stupidity - I was just lazy and didn't clean my Camelbak on schedule. I hit the water heavily during a hot-weather prolonged extrication, then had an embarassing moment when the contaminated water sought the fastest way back into the ambient environment.
Now I have two Camelbaks, and if one is getting iffy and I don't immediately have the time to clean and disinfect it, I just switch to the other one.
I agree with the use of vinegar. Safer that chlorine and will not harm you if it still tastes like vinegar. Wash, scrub with a brush and rinse EVERY PART, EVERY TIME it is to be used.
One hiker suggested to me the use of mouthwash for germ killing but I think Vinegar is more effective. You'll learn the value of effective rinsing, LOL.