I miss the old water bottles they sold in the local bike shops and sporting goods stores in the day. Pull the spout open with your teeth and push it closed before replacing in the cage. Modern bottles make the spouts more complicated than they have to be and they are perfect breeding grounds for mold.
By the way, it was mentioned in another water bottle thread about all the crap that gets thrown up from the road onto downtube mounted water bottles so if you think about that, the mold may not seem so bad.
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"It is the unknown around the corner that turns my wheels." -- Heinz Stücke