Thermos input, on which a coffee or tea coating was settled, can be cleaned with baking soda or ordinary baking powder (Just dissolve one pack in a small amount of warm water).
The fluid should be left in the thermos by 2 hours, then rinse it thoroughly. Remember too, to always store the thermos – It won't smell ugly for a long time. You can remove the musty smell, throwing into a thermos 1-2 coal tablets.