On Jun 19, 10:29 am, " > wrote:
>
> I tried washing it out using a narrow brush, but the marks remain. Is
> my thermos permanently stained? Or worse, was the steel pitted by the
> acidic coffee? Is that possible?

I ended up using a cleaning product called "Dip-It", and it worked
great. Removed all the stains, the interior of the thermos is shiny
and bright as new!