Here's How You Can Finally Erase Coffee Rings On Your Mugs With A Dishwasher Tablet - Tasting Table
Dissolve a dry dishwasher tablet piece in warm water, soak stained mugs overnight, then wash to remove stubborn coffee stains from ceramic, porcelain, and glass.
The Unexpected Way To Clean Coffee Stains From Your Mugs - Tasting Table
Denture-cleaning tablets effectively remove coffee and tea stains from mugs and other kitchen items using a gentle hot-water soak, are inexpensive, and widely available.