Urnex TABZ Carafe Cleaner
Urnex has a special formula to remove coffee oils and mineral deposits from brewers and vessels. The best way to see if your thermos needs cleaning is to use hot water, let it cool, then see if there is a taint of coffee or an off flavor. If so, you probably need some cleaning, even if there is no visible residue. 120 tablets per bottle. This will last you a long time.