I discovered this neat trick an hour before setting off on a climbing holiday after finding that my CamelBak hose was disgustingly dirty.
Being loathe to spend £20 for a brush on a wire to clean the hose and without time to get one I looked around for something that could clean the hose.
Paracord was the answer! A loose knot in the end of a length of paracord, dropped through the hydration bladder's hose can be drawn through slowly and bring all the gunk with it.
Here's how I've done it ever since.
Step 1: You will need....
Step 2: Soak
This softens up all the dried on gunk growing on the inside of the tube.
Don't pour the water away once the hose is soaked, save it for when you're finished cleaning the hose with the paracord then you can steralise the paracord before drying and storing it.