I had my diesel fuel tank repaired on the 89 gq 4.2 diesel wagon as it was leaking around the spigot the drain plug screws into. I pulled the sender unit out to make sure tank was clean inside before re installing it but there is a half size ice cream container size plastic box container free floating around in the tank that is not connected to anything.

Is this normal or has it come adrift from something?

What does it do?