I have run into this problem before and have yet to get an answer. I just acquired a Honda CL450 with a tank that has been kreemed and it is peeling out. Does anyone know how to remove this stuff so the tank can be used again?
Had the same problem on a T500 tank a few weeks ago.
At first it seemed to be just half full of really manky fuel. After emptying and then adding 500g of caustic soda to rhe tank full of water and letting it soak for a couple of days, I was a little pissed off to find someone had already lined it and was now coming off in strips. Also tried the pressure washer but made little difference.
So next attempt was to use the caustic soda again this time leaving it in for 5 days, and after draining and rinsing added 4 litres of water to the tank followed by 500ml of Spirit of Salts. Left it in for an hour making sure I kept turning the tank every few minutes. This stuff is more than bit dodgy to use so you need to be careful, certainly don't want to get it on paintwork.
Finally made sure the tank was thoroughly rinsed and dried as quickly as possible to avoid flash rusting.