When we start our pump it kicks on high and starts drawing in water. I then open up the air relief valve on top the filter. Soon after water begins to flow through the relief valve so I close it and can see water flowing through the pump. Then, we can wee the skimmer basket becomes empty of water as the pump is drawing it in, allowing air to enter the system. I have the pool filled up over 1/2 the skimmer intake so not sure why this is happening. How can we remove air from the lines?