Any ideas as to what this is and where it goes as its clearly not coming out. Mc18

Hmm, Im not even sure how that would have gotten in there?

The inside of the tanks are rather simple. And being that the fuel feed is simple gravity feed via a petcock, there is no large hole at the bottom for a fuel pump. The biggest hole is the fuel fill hole so one would think that what goes in that hole should come out that hole.

There are some overfill tubes that run from the filler mouth area, down through the tank and out the bottom.

Outside of that, there is no mechanism to monitor fuel level (two stage petcock tells you when it's time to move to reserve and get more fuel).

That looks like some sort of disperser. If the bike was previously used for racing and needed a quick refuel, that thing looks like it would spread the fuel, the part you hold in the vid would go inside the refueling nozzle. It also looks as though it may have gone brittle over time, so it may have been flexible when it was put in but obviously no longer is.