Man, I dunno.
I have mine mounted:
Inlet to the LEFT
Outlet to the RIGHT
Unconventional, but I have never had the issues that so many have priming these things.
One thing that I would recommend is NOT hard plumbing these things in. I find that some silicone hose and QDs so that you can fill the line with water, via gravity, goes a LONG way to easy priming.
It takes me about 10 seconds to prime my pump for a brew session, after it is primed, I dont have to prime it the rest of the day.