Thanks Waste! I think I figured it out. I did go out and buy some long bicycle valve stems to make the plug. The main drain and skimmer lines are together and I think the second port that come out in the skimmer is tied to main drain. I will make the plug using the valve and try to blow out the whole system from the skimmer. I just better get moving since it is going below freezing tonight. I was hoping to insert the valve in a 1/2 drain plug that I have on the supply line right next to the inlet of the pump but I don't think the plug is thick enough to drill and tap for the bicycle stem valve.
Amir