Problem: I left orange juice in my CamelBak for about 3 months! It went black and gunky and was seemingly impossible to get out of the clear drinking tube.
Fix: The credit for this excellent idea has to go to my Step-Mother. She said “Can’t you pull a bit of string through it with somethign tied to it?”. Well… that was quite a good plan, but I thought a better plan was to use a steel brake cable, and a small round piece of towelling threaded onto it, held in place by the pressed thingy on the end (if anyone knows what this thingy is called, please leave a comment!). Then just pull it through the tube backwards. I found that doing this twice after soaking the tube in Milton got all the scum out.