I plan to add solar collectors on the roof to heat my pool. The solar pipes go underground from the equipment pad to the exterior wall of the house and then go up to the roof to the collectors. So the underground pipes basically form a U shape with two upward openings at the equipment pad and the exterior of the house. My question is how to get the trapped water out of the underground pipes for pool closing. If I leave the water inside the pipe, is it going to develop mold or algae over closing months? I live in San Francisco bay area. Although it does not snow, there are certain months that the temperature is too cold for me to use the pool.