Rinse the cup with warm water
Sprinkle baking soda on a damp sponge
Scrub the stain gently
Use white vinegar for stubborn stains
Soak the cup in a mix of vinegar and warm water
Let it sit for 15 to 30 minutes
Scrub again with a sponge or brush
Use lemon juice and salt for natural cleaning
Apply a paste of baking soda and water
Rinse thoroughly with clean water
Wash with dish soap
Repeat if needed for old stains