It didn't come from in there...not a "check ball".....
It came out from one of those 3 valves.....
I remember when I took off that cover to expose the valves, it kinda just flopped out and I couldn't tell exactly where it came from.
I set it aside to ask about it and totally forgot.....
If it's a 1/4 inch diameter ball it an only have come from inside the VB. There are no check balls behind any of the valves, not even after installation of the TF-2.