Tea stains won't have a chance to form if you give your mug a quick rinse after you finish your beverage. Even if you can't wash the mug right away, rinsing will remove any lingering drops of tea. However, it's natural for tea stains to persist even after multiple washes. In that case, try soaking the mug in white vinegar or lemon juice for a few minutes, then wash it with a mild soap and warm water.