Purchased home with IGP--Noob looking for advice

Yeah, Bama. That's the only feeder I have. Why they set it up like that, idk. I don't know if it was a main drain at one time and they converted it or if it was ever set up as a main drain. The guy at the pool store said they aren't even installing main drains in most pools anymore. This pool was installed in 2004.
 
The MD/Hole is located at the bottom of the deep end in the middle. The size and shape is exactly the same as the the returns. The only difference is that there aren't any guts inside like there are in the returns (the ball for the jet). I can see water pushing up and air bubbles coming to the surface. It's very easy to notice water coming out of this thing. It seems to be just another return located at the bottom of the pool.
 
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