[Richard in Anaheim CA]

I had the same problem from gas left in the tank for 9 years. It looked like permatex.

A friend suggested since it was gas, maybe gas would desolve it. Intreresting theory. I drained what was left in the tank and put fresh gas in and rocked the car every time I thought about it for several days.

It did start the process, albet slowly.

I drained it and dumped in two gallons of carbuerator cleaner, heated it with a shop quartz light over night and then flushed with water using a strong garden nozzle. It worked. Even the gas float disappeared.

My final sequence was Por 15 Marine Clean diluted 50% and heated with a shop quartz light overnight. It got about the temperature of hot coffee.
I rocked it around, drained it, flushed with afore mentioned nozzle and it was clean enough to eat out of. Replaced float with wine bottle cork.

I wasn't about to remove the tank and the paint.

Richard
Anaheim CA