Make a solution of equal parts of distilled vinegar and water. Pour the solution into the container and leave it to soak for a few hours. When the time is up, drain the solution, then wash and dry it as you normally would.
3. The Sun
What better natural cleaner than the sun? Rub some lemon juice into the stained container. Then leave the container in the sun for a few hours. Wash and dry the container as you normally would.