Urnex Tabz 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 flavour. If so, you probably need some cleaning, even if there is no visible residue. Follow the instructions on the back of the label to best clean your brewer. 120 tablets per bottle.