Baking soda and vinegar are excellent at killing germs and wearing down stains when acting together. [2] X Research source It’s important to use distilled white vinegar, as it’s more acidic and will result in a better cleaning. It’s also less likely to leave a lingering odor or taste in your flask, which other types of vinegar may do.
Baking soda and vinegar are notoriously reactive. Putting the cap on the flask with both substances inside could result in a messy leak or even damage.
For especially thick buildup or heavy discoloration, give the vinegar and baking soda longer to set up.
A basic bottle brush only costs about $5, but it’s a very useful tool to have on hand for difficult cleaning jobs. Be sure to run your bottle brush through the dishwasher after using it to clean a stained flask.
Pat the body, mouth and cap of the flask dry with a clean towel, or let it sit and air dry. Give the opening of the flask a sniff. If you can still smell vinegar, rinse it a few more times, or fill it with hot water and let it soak, until it’s odorless.
The type of bagged ice you can buy at the grocery store is perfect for this task. If you only have access to large, smooth or rounded ice cubes, you can break them up into a more effective size yourself by placing them in a plastic bag and crushing them or throwing them in a food processor.
Use an extra half tablespoon (about 7ml) of salt if its a finer grain. Ice that melts in the flask may dissolve the salt, making it less useful for cleaning.
The salt and ice combination will essentially act as an “exfoliant” for the walls of the flask. Don’t worry about damaging the metal that your flask is made of. They’re designed to withstand extreme temperatures, mild impacts from being dropped and general wear and tear.
Using ice and salt to wear down stains is a safe, natural solution. Both ingredients are non-toxic and don’t contain chemicals that may be harmful if ingested.
A pack of denture tablets will only run you a few dollars, providing many uses in cleaning your well-used flask. The dissolving action of denture tablets also has an antibacterial effect, sterilizing the flask as they clean. [11] X Research source
Swish the water around inside the flask to make sure it’s completely wet throughout. This will help the sodium bicarbonate react on all parts of the flask’s inner surface.
A good general guideline is to use one tablet for every two cups of the flask’s volume.
Denture cleaning tablets are one of the safest and most effective ways to clean a dirty flask or thermos. All you have to do is wait. Once the reaction has died down, you can go over the inside of the flask with a bottle brush for a more thorough clean.
Putting the cap on your flask while it’s still wet will encourage bacteria to set up shop inside.
