Since their introduction in 1946, Tervis tumblers have been known for their fun designs, lifetime warranties and, best of all, their ability to keep hot drinks hot and cold drinks cold. The tough plastic tumblers are safe to use in the dishwasher, freezer and microwave. However, like almost every other type of drinkware, they're not impervious to tea stains. According to Tervis, a couple of simple hand-washing techniques should do the trick.
Fill a sink or washing tub with warm water and add a generous amount of liquid dish soap.
Soak the tumbler in the soapy water, then wash the cup thoroughly with a soft cloth. Rinse and dry the tumbler.
Sprinkle a small amount of baking soda onto a clean, wet cloth if the tea stain remains. Wipe the inside of the cup to remove the stain. Rinse and dry the tumbler.