Below, you will find some pictures of a closed return, open return with a rubber plug, and the front and back of the actual cap that is screwed into the return jet. The threads are broken inside the return housing. Ironically the person who closed the pool today stated that there is air leaking outside the perimeter of the black rubber plug. I have confirmed the leak as we pushed air through the system for a split second with the Cyclone (rubber plug was still intact) and bubbles of air were released. Somehow, the return is designed to be closed without a rubber plug, the rubber plug fits nicely, but not with the cap. You can do either one or the other (if this makes sense).
What I do not understand is the design of this system. There is no way of repairing from inside of the steps and I assume there are threads on the outside of steps, which of course is buried in dirt and concrete. He may lower the water, remove rubber plug, apply silicone all over the inside of the cap and hold from one side to another with a tension bar. I even suggested an "air lock, but there is no shut off valve. I could plug the inside of the basket at the pump, creating an "air lock" after air is blown out again. The only issue with this is that the water would not remain under the frost line, which is 36" (which I have confirmed), but some of the plumbing should be there. Hard to tell because everything is closed off.
Anyone have any thoughts for repair, prevention, etc? You cold lower the water below the return and the safety mesh cover will have a solid cover with a pump so water will not fill up in the pool, but drain away from the pool.