Rinse well with with hot water a few times. Avoid using soap as it will get absorbed into the walls of the cup and distort flavors. After rinsing it with water, shake well to discard excess water and dry with towel. Store in a dry place
Before first use, it is a good idea to 'season' the cup. To do this, brew 6-7 ounces of tea or Yerba Mate at double strength. Pour into cup and soak for a few hours.
If a lot of time passes before using the cup again, repeat this process as to prevent cracking.