Klean Kanteen has a website that covers these methods - some of the suggested tactics work better than others. Check out the following methods and learn which ones work best.
Step 1: Take me to funky town
juice and or coffee + hot car + time = FUNK
In the image below we left this insulated Klean Kanteen in the car for a few days with tea in it. When we opened it up there was mold everywhere growing on not only the tea bag, but the walls of the water bottle themselves.