You may have a plastic Thermos that you use frequently for soups, hot meals or coffee or tea. Over time the Thermos can develop an odour. Don't toss out your beloved Thermos, just get rid of the smell. It will only take a few minutes to restore your Thermos to its previous normal-smelling state. Cleaning your Thermos daily and deodorising it weekly can keep odour from building in your plastic Thermos.
Pour 2 to 4 tbsp of baking soda into your Thermos, depending on how large your Thermos is.
Fill the Thermos over halfway full with hot water, and replace the cap on the Thermos.
Shake the Thermos to combine the hot water and the baking soda, which will form a natural deodoriser.
Pour the baking soda and water mixture out, and rinse the Thermos completely. The Thermos should be completely deodorised and odour free. Repeat as necessary.
If your Thermos is really stained or stinky and a few shakes won't do it, soak the Thermos with the baking soda and water inside overnight.