The vinegar and baking soda mixture will froth up, so be sure to put the flask in the sink when you combine them. [substeps] Baking soda and vinegar are excellent at killing germs and wearing down stains when acting together.
[header] How to clean a vacuum thermosflask that has stains at the bottom [title] Put some baking soda and vinegar into the bottom of your flask. [step] Pour about half a cup (120ml) of distilled white vinegar into your stained flask. Then, shake in approximately one tablespoon (15ml) of baking soda for every cup the flask holds.