What is a good method to clean stainless steel hot water pot?
Wow! That is quite a patina you have built up there.

I would try Barkeeper's Friend (oxalic acid) in a thick slurry and soak it for a day and see what happens to remove the blackening. It still won't remove the orange enamel paint though. So you might end up having to wet sand it after taking it to a wire wheel.

Sound like a project.