1965 fury gas tank question

I started the process of resurrecting my 65 fury the other day. I dropped the gas tank, was full of a real lot of sludge. I bought one of those 3 part gas tank restoration kits on eBay, since a new tank is no longer available. My question is, is there anything stronger I can use to clean out the tank than the cleaner they supplied me as the step one to the kit, because this stuff has been soaking in the tank over a day and upon looking in the tank this morning with a flashlight this...

1965 fury gas tank question
Author: 65fury1