I clean my drinking system with lots of hot water then sterilise it using baby bottle sterilising tablets.
Once it is clean, I don't dry it - I store it in the freezer. :-)
Additionally, I don't use anything but water.
People
I know who use powdered drinks or sugar solution tell me the black mold grows really quickly inside the drinking tube and valve.
outdoors.stackexchange.com/users/3079/Greenstone Walker
Drain all the water out of the tube Remove the tube from the bladder and the bite valve and hang it up Bend a metal coat hanger in half (make sure no sharp edges are exposed) push the coat hanger into the bladder and hang the coat hanger up You can also buy airers but the coat hanger works just as well.
From a cleaning point of view you just need baby bottle steriliser and some brushes.
The clean the inside of the tube you can by specialist brushes, they're a brush on the ned of a flexible wire.
outdoors.stackexchange.com/users/None/
I bought a water reservoir cleaning kit for about $7 from Walmart.
Disclaimer: I haven't used it yet
(I only got it a month or two ago.
I haven't gone on a longer hike where I wanted to go to the effort of filling a water reservoir, instead of just bringing a little bottle).
Outdoor Products
Hydro Cleaning Kit
It came with a cleaning brush for the tube and one for the reservoir itself, but most importantly for this question, it comes with a little coat hanger type piece of plastic (similar to Liam's method above).
You fold up the coat hanger thing, then push it into the reservoir and let it pop back into shape, then hang it up.
Before, I always ended up going to a lot of effort to try to balance the reservoir with the hard opening vertical and the rest of the bag
flat, so some air could get in.
It would always flop flat after a few hours, or someone closing a door in the next room, etc.
I'm looking forward to not doing that.
outdoors.stackexchange.com/users/3945/nife
I drain mine thoroughly, hang/suspend it with the open end down, and stick an empty paper towel tube stuffed with paper towels into it to keep it open.
I've found that if I only use water, and let them air dry promptly, I never have a problem.
I only use filtered water in my bladder.
If I feel I want to clean them, I use a warm white vinegar water solution and rinse and flush that way.
outdoors.stackexchange.com/users/9928/M Kenyon II
take a fish tank pump or air mattress pump and run a plastic tube into the bladder.
It circulates air and takes about 30 minutes.
For the tube itself, I remove the bit valve off the end and swing it around to get the centrifugal force to get most of the water out--then I use the pump--takes about 5 minutes.
outdoors.stackexchange.com/users/9916/user9916
When I need to wash a drinking water bottle, canteen, bladder, etc.
I fill it part way with warm water, and add table salt.
This particularly effective for areas that have growth or contaminates and can not be effectively scrubbed.
Add lots of salt, to the point of saturation (when shaken salt still settles to the bottom)
, Shake well.
Most anything that grows well in drinking water gets killed by high levels of salt.
The additional salt works as an abrasive to remove build up.
You can let it sit for a couple of hours, or overnight.
Rinse well and hang upside down to air dry.
For soft sided containers you may need to use a clean item to keep it from collapsing as mentioned in this answer by M Kenyon II
outdoors.stackexchange.com/users/4079/James Jenkins
After using water bladder, how to dry it thoroughly besides simply pouring out the water content so any remnant of water inside it is cleanly eliminated?
How to effectively dry/clean the inside of water bladders?
outdoors.stackexchange.com
<hydration-bladders>
outdoors.stackexchange.com/questions/6628
outdoors.stackexchange.com/users/3857/qazwsx
Drain and hang it upside down. A bent coat hanger can be used as a drying rack. The tube is cleaned by removing the bite valve, swinging the pipe and then using a pump to remove excess. Some people clean it using warm water and salt and others use baby bottle sterilizing tablets. Air drying, as well as warm water and salt/sterilising tablets, are effective.
Air drying works with various techniques. You can fill with warm water and add salt/sterilising tablets.