You can try making a paste of Baking Soda/water and using that. If that doesn't work you can take off all the coating using the usual methods of steel wool/Brillo/SOS pads, liquid/powdered stainless steel cleaner to get rid of everything followed by a really good scrubbing using Dawn and hot water. Then rinse it well with boiling water. Then make a cup of Black tea with a really long steep time, with-out the tea. i.e. Fill'er up with boiling water and let it sit for 5 or 10 minutes. Then dump and rinse with more boiling water. Repeat the boiling water soak/dump/rinse cycle at least one more time. Any residue should now be gone. If it's the totally clean/oxide free taste you object to then you'll need to season the cup with a throwaway, filled to the top of course, cuppa that you let sit for a good period.
Java "That should do it!" phile