You mean thermos?
Just came across my mind, how about denture cleaner tablet? Add a tablet or two and water and soak overnight and rinse well.

Hope this helps!

Yep....denture cleaner.
And rice shaken in it with a bit of soapy water is pretty good.
AND....they make a bendy cleaner thingey...like a long very fat pipe cleaner that works well.
Unfortunatly I don't remember who "they" are that make the thing!
Linda c

Baby bottle brush! That's what I use on my thermos. Mine is stainless steel inside. If I've let it go too long (hard water maybe)or it dried, then I soak it, and I cut a piece of scotchbrite, the thin kind that is not on the back of a sponge, center it on the tip of the baby bottle brush and swish around with that. It gets the residue right off. Since it's thin if it falls off you can still get it out.

I use a Thermos for "cooking" beans, grains, and oatmeal in, and it can be a real mess - especially from black beans or oatmeal. I use the denture tablet method. Even better than a baby bottle brush (which was too short and not stiff enough to clean my Thermos), I found a long-handled kitchen gadget with a sponge on it (you can also put soap and water - or other cleaner- in the tube of the handle). This gadget has the perfect size and shaped sponge, and handle length, for getting inside the Thermos.

-Grainlady

A couple spoonsful of baking soda in hot water overnight will get rid of the coffee stains.