This is a shot inside my kettle that brown scum don't move. I give this a scrub and rinse before brewing but I'm sure that brown stuff is more like a protective coating now for the stainless? I'll also scrub her out quick at end then up end her somewhere out the road till next session. Don't mind my dodgey dip tube I didn't kink it but went real close I filled it with sand first as I've herd this helps.