I use Bottle Bright tablets when mine gets looking like that. I heat up water in the kettle to almost boiling then fill the thermos and drop a tab in for at least 30 mins. I've even left over night on tough ones. Its worked on everything I've tried it on. Plus it's non toxic.
hipstr_doofus t1_j8uug7d wrote
Reply to Cleaning a thermos bottom from coffee traces "properly". by iBo0m
I use Bottle Bright tablets when mine gets looking like that. I heat up water in the kettle to almost boiling then fill the thermos and drop a tab in for at least 30 mins. I've even left over night on tough ones. Its worked on everything I've tried it on. Plus it's non toxic.