Getting ready to assemble the fuel tank and while moving it around on my work bench, I heard something rattling inside. Fishing with a coat hanger, I finally got a hold of it. I had to cut some chinks off to get it out the fuel sender hole.
Based on the edges, it had been sloshing around for a wile. One edge, the plastic was shaped to snap into something.
I hope this is not part of the tank.