What is in my fuel tank?

[In The Ten Ring]

My fuel tank was sandblasted inside and coated with "renew" which is a teflon-impregnated rubber substance. I covered up and sealed off all openings, installed it back into the truck, and stuffed a rag into the fuel filler neck, within days of that I hooked it back up to the fuel and vent lines. For the past year, it has had a gas cap on the filler neck.

Today I peered inside.....there is a coating of yellow powder inside the filler neck. On the ribs inside there, are two white spots.

I called the company that did the renewing, they are equally at a loss. The man did suggest removing the tank and bringing it to him and that I unhook my fuel line and run a hose to a gas can for starting the engine (my next truck goal).

What could this powder be? Pollen? Mold?