Anyone know what this is?

Sorry, it is tough taking a picture of it with the reflections from the sun.

It appears to be about a 2" pipe feeding into the side of the skimmer (near the top). There is a cover over the pipe with a black nipple sticking out into the skimmer basket area. If you look above the red arrow, you can see the threads where the pipe comes in. It has a screw-on cover with the nipple part.
 
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