Recently bought house with a pool. I know the layout of my plumbing for the most part, but I’m curious what that pipe with the black nub coming out is. Also the little capped stub out on the return side of the pool.
@ajw22 nailed it. Old Polaris plumbing. The capped 90 below the diverter valve was likely for the inlet side of the booster pump, and the black fitting is for the flex hose on the outlet side of the pump.
Welcome to TFP! For a wealth of pool care information please check out our free Pool School. If you are in need of specific help then we encourage you to Register and ask us here in the forum!