I fill an Aladdin Stanley quart stainless vacuum "thermos" every day for home use. After a few months a brown scum forms on the inside. I use a partial tablet of automatic dishwasher detergent and boiling water, fill, shake it up and let sit overnight and rinse with hot water (several times) in the morning. The coffee residue will come out as kind of a brown film. Looking down at the bottom under a strong light, you can see it is now shinny stainless. Good to go until next time.