The most convenient way is: you have toothpaste and toothbrush at home. Squeeze the toothpaste into the toothbrush, first wet the cup with tap water, then pour out the water and brush it directly on the inner wall of the cup, slightly harder than brushing your teeth. Rinse with tap water after brushing. It is green. In addition, there are many tea stains, which have a great influence. China also has a saying, "If you don't wash your cup when you drink tea, the king of hell urges you to die."
Tea leaves that have not been drunk or put for a long time are exposed to the air. Tea polyphenols in tea leaves and metal elements in tea rust will be oxidized to form tea scale, which will adhere to the inner wall of the cup. "Tea scale" is the chief culprit that harms human health. Because tea scale contains toxic substances such as cadmium, lead, mercury and arsenic and carcinogens such as nitrite. I hope my answer can help you.