muratic acid is the way to go and is readily available! if you had your tank professionally cleaned they would steam it out and wash it with the acid!dodger said:I use Muratic acid on my old Puch mopeds I buy. The tank is part of the frame so it is diff. to clean. If you can remove the STEEL tank then soap and water and nuts and bolts to break the crap up. Do this a few times then rinse with gasoline.
Please don't try muratic acid on a plastic tank and be carefull....the stuff is nasty.