Most pumps are self-priming, but they will require you to prime the pump by filling the priming port and pump housing with water upon initial installation, to force any air out and allow for the impeller to start sucking water. Any air pockets left in the lines or the pump will cause the pump to become air-bound. An air-bound pump will not operate properly until the air is removed and replaced by water. As long as a check or foot valve is installed on the suction pipe and you never lose suction, you should not need to re-prime the pump. That said, the only pumps that we offer that can truly self-prime would be some of the gas diaphragm pumps that we offer like the Honda WDP30XK1AT - 80 GPM (3") Diaphragm Water Pump or the Multiquip MQD2H - 50 GPM (2") Diaphragm Pump w/ Honda GX Engine for example. You can watch the video below to learn how to prime almost any pump.