When the pump shuts off the liquid sitting in the pipe up to the ceiling level can drain back to the level of the pump. Theoretically this will reduce backpressure on start up.

It seems unnecessary to me but I am not a licensed plumber.

Tom W

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.