I'll second Rowan's question.
Why do people find it so difficult to clean water bladders?
I just use dishsoap and water like I would any of my dishes. Add soap, add water, swoosh it around a bit, let it sit for a minute or two to kill any bacteria, then rinse. Make sure soapy water flows through tube, and make sure the tube gets rinsed as well.
If I'm just drinking water out of it, I don't even bother cleaning between uses, I just store them in the freezer.