That looks neat but once you start running water, it will not fill up as the nozzles are facing downwards.It is hanging like this but is level. There were no instructions with it at all. Everything was guesswork.
There will remain quit an important air pocket inside.
If that is the only mounting position possible, you might take it off, connect the hoses with the nozzles upwards, run water through it and put it back in position without disconnection the hoses.
At least that is how I did it when I was in the same situation.
But even then you might have air entering after you restart the pump.