Looking to get a backup sump pump and noticed all the manufacturers rate GPM based on how many feet of "Lift" is required. I have a 1.5 discharge line that goes up about 8 feet and then travels downhill about 100 feet. (It's 1.5" the whole way) When the pump stops I can hear air sucking from the pump until all the water drains from the line. To estimate the GPM a backup pump will give me do I only need to consider the "Lift" or is there friction loss for the downward travel ? Or would it actually achieve better performance because a "siphoen" effect is created ?