When we first had our pool built, the builder showed me to 'lock in the prime' when turning the pump off to clean the basket. I would turn the valve so that the 'off' portion of the handle was facing the pump. Anyhow, I've noticed lately that this no longer works and when I open the top of the basket, I hear all the water flush back. When I restart the pump it take about 2 minutes to refill and be back to normal. Is there some way to correct this and does it damage the pump, even though it says 'self priming'?