Most transfer pumps move liquid from one tank to another and are self-priming. However, there are some pumps that require priming to get started. Priming is necessary because these pumps work on the principle that water escapes from high pressure areas to low pressure areas. Unless the pump is primed, the pressure isn't high enough to pull through the more pressurised water. This is why it is necessary to increase the pressure with outside air.If you are applying primer, you should not have a connection between the transfer pump and its destination.Push the priming pump onto the closed fuel line.Bolt the pump using the attached bolts and gaskets.Press the fuel pump down a few times to increase the pressure in the transfer pump.Remove the fuel pump and close the fuel line. Now the transfer pump is ready to function on its own.