New Gasoline tank interior coating

[TexasMax]

I purchased a new metal gasoline tank for my lawn mower (1952 8N Ford tractor. No instructions included. I installed and all was well for about 1 year. I started tractor and began using the finish mower. The tractor stopped running and when checking gasoline I noticed some kind of plastic, vinyl or epoxy coating was floating in the gasoline and stopping up the filter screen. This coating was a protective material the manufacturer had used to supposedly prevent rust during storage of new tanks. I was supposed to remove it before use but no instructions to do that. I removed tank, emptied gasoline and tried naphtha but no results to remove remaining.
What should I use? The gasoline did not turn all of the coating loose.. Thanks.