This is the first season with the pool. The pool has two returns- one has a 3/4" eyeball (at the front corner of the pool), the other has nothing (at the side of the pool-this one is several inches deeper in the water than the other). I never thought much about it and figured that's how it was intended, but I looked at it closer and noticed there were threads to screw in an eyeball. Is there a reason this one would not have an eyeball?