No matter how often or thoroughly you clean your thermos, there's always the chance of mold getting in there. This doesn't mean it's curtains for your favorite thermal drink container: Cleaning the mold out of a thermos is a cakewalk, and it shouldn't take you more than a few minutes.
Step 1
Rinse the thermos with hot water to keep the mold wet. This will prevent spores from flying into the air while cleaning and will make the mold easier to remove.
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Step 2
Mix a little bit of bleach with water and let it sit in the thermos for five to 10 minutes. This will kill the mold.
Step 3
Empty out the bleach/water solution and rinse out the thermos.
Step 4
Wash the thermos with dish detergent and water, using a sponge or scrub brush to scrape away any mold that's still inside the thermos.
Step 5
Dry the thermos thoroughly, making sure there's no leftover mold. Your thermos is ready to use again.