Mounting external pumps upside down?

[beaker020]

hmmm...just thinking out loud here. If the outlet is down you may have a problem on startup. Typically, when first installed, before the power is turned on, the impeller is dry. When the valves are turned on the impeller is flooded and the incoming water pushes the air out the outlet on top. If the outlet is down the air may not have anywhere to go so the pump may start up dry. It should push the air out soon enough in a big cloud of micro bubbles but it may cause an air lock.

I've never tried it but like I said, I'm just thinking out loud.