I also noticed the chemical stench.. I used hot water and dish soap and my bottle brush and scrubbed for a few minutes and it went away..

For the hot weather, I fill 95% full and freeze overnight.. I take it out about 1-2 hours before ride, because it will be a little off balance.. It thaws enough so I have cold water for the 2 hours that I am riding..

For rides with 2 bottles, I take one out of the freezer 2 hours before and the next 45 minutes before the ride and I always have cold water for the whole ride..