If your kids back to school thermos is stained from Summer use or your trusty morning thermos is showing remains of drinks past, you can clean it easily. Fill the thermos about one third of the way with warm water. Add 2 drops of dish liquid and a handful of crushed egg shells. Secure the cap and shake for 2-3 minutes. The abrasive shells combined with the soap will break down the stains. Rinse and you’re all set to fill with your favorite beverage.