First clean the cup with detergent, then pour the boiling water into the cup for two hours, then clean the cup.
If there is rust in the cup, pour some vinegar in the kettle and brush it gently with a soft brush. Use vinegar to fully touch the rust. If there is stubbornness, you can pour some hot water to continue scrubbing. After the rust disappears completely, Rinse with water.
Potato descaling method: Put a few potatoes in a pot full of scale, cook for a few hours, thick scale will fall off on its own, and the body will not be damaged