I had trouble priming my pump. After verifying that the pool level was sufficient for the skimmers and the replacement of the pump strainer o-ring, I was able to start the pump by isolating water to the pump with only the main drain and vacuum lines as input. The pump now runs without any bubbles when the skimmer feed valve is turned off; the valve is positioned just prior to the pump.

Between the skimmers (2) and the pump is a Pentair check valve; my pump is 4' above grade. I've applied fresh silicone to the check valve cover to no avail.

So, I'm looking for recommendations to determine how to troubleshoot the suction leak on the skimmer side input to the pump. So, is there any way to leverage the fact that there is a check valve between the pump and skimmers and if so, how?