One more thought, based on my Gremlin like experience from last night, use drain valves that can't easily be bumped open. We had a major storm here last night and a small limb fell from a pine tree in the middle of the night , and just happened to hit my solar drain valve see picture below, knocking it half way open, as a result by mid morning the skimmer was sucking air. Therefore I have now wired the valve into the closed position.
Ike