I have heard other owners talk of adding rice to the mix to act as an abrasive when draining out the tube. While mine does get drink mixes I have to clean it out after each ride so it only gets used as a drink holder for rides which will be long enough to need that much because I only carry one bottle. The mixes also serve to mask any flavor issues, although I can't say its been a problem.

I always hang the bag out upside down to drain with the bite valve out and something inside the main bag to keep it open. I use two clothes pegs clipped together but a bent coat hanger would work too.

As a side note, on longer organized rides I normally keep an empty bottle in the cage for the drink stations. They dont always have cups so this keeps me from having to take everything off unless I'm refilling.

Andy