Apparently have a leak in skimmer line, I can valve off either the skimmer line or the main drain line. With both lines to the pump open it sucks air, with only the main drain line open I get no air to the pump, with only the skimmer line open it sucks a considerable amount of air to the pump. I've checked the lines above ground for leaks using methods described on this and other boards and found no problems.
I have never gotten much movement of water from the skimmer located furthest from the pump, I have valved off the line from the skimmers to the pump and blown water from the garden hose and 90psi compressed air betweed the skimmers. I tried pulling water from the furthest skimmer with my large wet dry vac and could only get water out after I hit the line with compressed air. After I did this the air stopped coming in for a day then resumed.
How deep are these lines to the skimmers normally buried?