I use a dilute bleach solution, 1/4 cup bleach in a gallon of hot water, in the sink to sanitize my water bottles, when they're looking dirty after a wash. To be sure the straw is clean, I soak a chenille stem (big pipe cleaner) in the bleach solution and run it through there straw to listen whatever may be stuck inside. I also use the chenille stem soaked in bleach solution to clean out the inside of the mouth pieces. I let everything soak 30 minutes and then rinse with hot water. All parts are allowed to air dry on a clean towel.
Hope this works. I get my sterilizing and cleaning techniques from working in the food service industry.