How to Clean a Thermos

Using Baking Soda and Hydrogen Peroxide

Add 1 in (2.5 cm) of hydrogen peroxide to the bottom of your Thermos. The mixture will foam once you add the final 2 ingredients. Leave enough space so that the Thermos does not overflow by adding no more than 1 in (2.5 cm) of hydrogen peroxide. You can purchase 3% hydrogen peroxide at any local grocery store.

Put 1 US tbsp (20 grams) of baking soda into your Thermos. Baking soda, or sodium bicarbonate, is extremely useful for de-odorizing and whitening. If you are cleaning a larger Thermos, you can add an extra 1 tbsp (20 grams) of baking soda. Ideally, you should use 1 US tbsp (20 grams) of baking soda for every 2 cups (470 mL) of liquid that your thermos can hold.

Fill your Thermos ¾ of the way with boiling water. To properly activate the baking soda, you must use hot water. Make sure to add the boiling water to your other ingredients as soon as possible after adding the baking soda. The mixture will foam slightly.

Let the mixture sit overnight. Allow the mixture time to work so let it sit overnight to get the best results. If you would like to clean the lid of the Thermos, place the lid sideways on the top of the Thermos so that the side you drink from is submerged in the liquid and allow it to sit overnight.

Rinse the Thermos under warm water and allow it to dry. In the morning, rinse the Thermos out with warm, running water. The mixture should come out easily. Leave your Thermos upside down to dry, and you are good to go. After rinsing out your Thermos, you can wash it as normal, but it is not required. To remove any leftover baking soda, scrub the bottom of the Thermos with a bottle brush.

Cleaning with Dental Tabs

Fill your Thermos ¾ full with warm tap water. You don’t need to make the water too hot. You can use warm water from your sink to fill the Thermos. Make sure to leave around ¼ of space between the top of the Thermos and the water.

Add 1 dental tablet to your Thermos. These tablets are made to clean and sanitize mouth appliances so 1 tablet should be powerful enough to remove even the toughest stains. You can buy dental tablets at any local drug store or grocery store. Any brand of dental cleaner will work just fine. If you have a Thermos with a smaller neck, break the tablet in half to fit it into the bottle.

Let the mixture sit for 5-10 minutes or until it has stopped fizzing. As soon as you add the dental tablet to the water, it will begin to fizz. For this method to work, allow the dental tablet to stop fizzing before cleaning it out. You will notice the fizz begin to settle in about 5-10 minutes.

Wash out the mixture, clean the Thermos with soap and water, and let it dry. After the dental tablet has stopped fizzing, you can go ahead and dump the mixture out into the sink. Wash your Thermos as you normally would or use a few drops of dish soap and warm water. Dry it with a towel or allow the Thermos to rest upside down. You can use a bottle brush to clean the inside of the Thermos to ensure the entire dental tablet has been removed. For tougher stains you may need to repeat this process.

Removing Stains and Odors with White Vinegar

Pour 2 capfuls of distilled white vinegar into your Thermos. You do not need to use a whole lot of vinegar to freshen and clean the Thermos. Make sure that you add enough vinegar to coat the entire inside of the Thermos. If you no longer have a cap on your vinegar bottle, add a splash of vinegar to the bottom of your Thermos.

Put the cap on your Thermos and shake the bottle for 30 seconds. The goal here is to cover the entire inside of the Thermos with vinegar before you add water. Check that you have securely sealed the cap on your Thermos before shaking the bottle.

Fill the Thermos halfway with lukewarm water. After the interior of your Thermos has been coated with the white vinegar, remove the cap and add the water. Do not fill it more than halfway. Lukewarm water is preferred, however, any temperature of water will work.

Scrub the inside of your Thermos with a bottle brush. You don’t need to spend too much time scrubbing the Thermos. Just make sure to scrub any stained spots to help loosen the stains. If you do not have a bottle brush available you can use any other type of cleaning brush that has soft bristles and fits into your Thermos.

Replace the cap on the Thermos and shake the thermos again. Shake your Thermos enough to coat the Thermos interior with the water and vinegar mixture. This will also help any stains you scrubbed loosen even more. This should take about 15 to 30 seconds.

Empty and rinse your Thermos thoroughly and allow it to dry. Once you are done shaking, remove the lid to your Thermos and dump out the water and vinegar mixture into the sink. After the Thermos is empty, rinse it out with warm water. You may opt to wash your Thermos with dish soap and water, but you do not need too. The bottle will not taste or smell like vinegar. If you still notice any stains, odors, or discoloration, go ahead and repeat these steps.