Many vacuum flasks manufacturers do not recommend washing the flask in the dishwasher. Check the care instructions to see if the flask is dishwasher-safe so you can simply wash it in the dishwasher after each use.
These areas of the flask can harbor mold if you do not clean them well, so do this every time you clean your flask.
For a heavily-stained flask, you might need to repeat this 1-2 more times.
If you’re in a hurry, use a lint-free cloth or paper towel to dry the inside of the flask and its parts.
Baking soda is cheap and easy to find. It’s usually located in the baking aisle of grocery stores.
The vinegar and baking soda will react with each other and begin to fizz. This will help cleanse the inside of the flask and eliminate odors.
The combination of lemon juice and baking soda should eliminate any foul odors and you may even end up with a lemony-fresh smelling flask.
You can leave the baking soda in the flask for longer than 8 hours. Just make sure to rinse it out before you use it again! Use a sticky note that says something like “Rinse!” and stick it to the flask so you remember to rinse it out.
