Well, I did see a large pic on a website, showing the bottom underside of the tank...and it looked like there was a "slice" (for lack of a better word for it) of
that piece, there. But there's no way the whole piece would be needed. Plus... someone already said the diameter of the piece is too large to even go into the tank. So...I'm totally stumped.
Only other thing I could think of is if some SA just included it in the parts baggie,
if there's one of those small blue-handled screwdrivers in the baggie, too. Maybe it's then a tool stand for it??? Handle sticking down into it and pointed end sticking up???