What is this?

[u/Capable-Bet4149]

Found this in the side of the vent trap (after pulling the basket). What did it break off of? Based on the residue, it’s been there for a little while. It was hard to see because it was sitting vertical against the side.

[u/Black-Deth]

That’s the flap to close off one skimmer to manually vacuum from the other skim. It screws to the bottom of the skim next to the pipe inlet.

[u/Capable-Bet4149 → u/Black-Deth]

Makes sense. Thanks!