My home has an above groung aerobic septic system and the farthest spray head is below the pump so water continues to flow or siphon after the pump stops. Is there some way to stop this free flow? - Thanks JJ

Google vacuum breaker and peek at how it works. Is this what you are talking about?
Or try this Atmospheric Vacuum Breaker Operation (http://www.dwbp-online.com/avb_flow.htm)