Because for too long often used, sometimes not smell foul thermos that is quite disturbing. To get around the stink, the people of ancient times typically uses egg shells and vinegar, lho. How, destroy egg shells and insert it into the flask in unison together vinegar, shake-shake the flask gently, and let stand several hours.
Egg shells serve as the basic crust busting thermos, while vinegar as a natural bacteria killer. Just with eggshells and vinegar, the flask can be reused without being disturbed by annoying scent.