On Swimming Pool Levels.... Alright, this should be a simple enough question. Per code, the pipe which feeds my swimming pools self-leveling pump has a valve to prevent back flow, so swimming pool water does not contaminate the residential main. However, the valve is located at a point physically higher than the peak water level in the pool. My question is, is this valve redundant? Since the pool isn't pressurized, it seems to me that the water would generally reach an equilibrium height in the piping equal to the level in the pool. Is there some kind of vacuum pressure or other siphon effect that would ever cause the pool water to climb higher and spill back into the system?