Yes it is. There is a two step chemical process that works pretty good and is fairly cheap. Yamaha makes it and Ive used it many times with very good results. On a heavily rusted tank you may need to go through the derust process 2 or three times.

How to remove rust from your motorcycle's fuel tank

Theres some good info here.

If you need anything else just give a shout.

 

Kream, an acid cleaning that you shake around the tank with sheet rock screws then a rubber like coating.