For a very long time I have known that the best way to clean my coffee Thermos is to fill it with warm water, drop in 2-3 denture cleaner tabs and let it set overnight. The next day all the stain is loose from the bottle and after shaking with the bottle half filled it is ready to go. I did the same for the chaff filter and used a tooth brush to gently scrub the filtering sides without the shaking and it did amazing too. Looked good as new.