how can i clean the interior of an electric airpot?

Question

On the wall of the airpot's interior, there is a coat of blackish stuff that cannot be wiped off. How can I remove these?

Answer 1

Fill the airpot with household liquid bleach
diluted with tap water. About 100 parts water
to 1 part bleach. If more concentrated it will
work faster but smell bad. Just let it sit for
about a half hour, then rinse it out with water.
The same removes coffee stains from cups
and mugs.

Answer 2

try plain white vinegar and let it sit. should rinse right out.