I have a unique set up.
First, my pool pump is in the basement. Second, I had until today solar panels hooked up to the system.
I had the solar panels removed, and drained the panels, but discovered that once they drained, water was still coming out of the value to drain the solar. If I closed main valve from the return, the water stopped flowing.
I think the diverter has one of those intentional holes to drain the panel even in the off position. However, with everything off, there's enough pressure from the return lines to flow water back through up the diverter and up and out through the drain valve when it's open.
I don't have any isolation valvues.
I have made sure the jandy value will stay off. But I am afraid if the I turn on the pump, water will start trying to go up the diverter. I am attaching a pic.
The blue tape is just me attaching a hose to the drain to go to my basement drain.