Sometimes the kids lose a sippy cup under the couch. Sometimes I don't get around to doing the dishes for a day or two. And sometimes I don't realize that a cup is missing until 2 weeks later, when it mysteriously turns up under the front seat of the car. Things get nasty quick in the summer. You know what you'll find inside. Before you toss them, give this a try. If this doesn't save them, nothing will. This is how you get that gross smell out of plastic cups and bottles.
You'll need: Baking soda, peroxide, vinegar, and dish soap
Measure out 1/2 c baking soda, 1/4 c peroxide, and 1/8 c dish soap
Mix it up until its nice and smooth
Drip it down the sides of the cup until everything is covered
Apply to the lids
And coat the valves
Let everything dry overnight. In the morning, move them to the sink and fill them with vinegar
Let them soak for a few hours. Scrub off the soap, and put them through the dishwasher. They should smell nice and clean!
Let me know how it works for you!