In reply to Bahrain:
Simply take the bite valve, and screw connection off each end (may need to immerse in warm water).
Take an approximately 3m a length of paracord (2mm diameter or so) and tie a small overhand knot in the middle.
Feed one end of the cord down the tube until comes out the other end and the knot is at the start of the tube; then carefully pull the knot down the length of the tube.
The cord ought to be long enough to enable you to pull it back the other way to get any bits it missed the first time etc.
This will scrape out the nasty mould. Then simply pull the cord out, wash it as normal and leave to dry.