Pat - If you hold the pump horizontally with the end cover (the black plastic cover with the power terminalcoming through it) pointing away from you and the inlet/outlet ports pointing to your right, the upper port is the outlet and the lower port is the inlet. this is how the pump should be oriented for the most efficient operation. Tony is correct that it doesn't matter, the pump will fnction in any position, but it is most efficient when oriented in the above position. Also, if you turn the pump so the ports are facing you and look at the flang below the top hat shaped cover at the top of the pump, you will see the words
OUT : TOP on it.
Cheers,