To remove seemingly impossible to clean coffee stains from stainless steel cup/thermos:
1. rinse with dish soap to remove majority of oils
2. fill with hot water
3. drop in 1 dishwasher tablet
4. wait 1 hour them rinse out with brush
This works better than vinegar + baking soda, denture cleaning tabs, and steel wool. You are welcome.

>>712587417
Thank you Doro