If air is flowing through all the lines properly, you may need to put some fluid in the pump and line to the pump. Maybe someone decided to cut corners and not use a self-priming pump.
First off I can see mineral deposits still in the cast pump base, all that green and white crud has to be goneOK, final weekend at getting this thing up and running...
My technical method for determining flow (blowing air through) hits a "block" when the brass colored piece (on the right side) goes back in its place on the opposite side from the fluid line. I'm not sure what this brass piece does but, it comes apart and has a tiny spring and tiny plastic piece. Since I don't think it soaked in vinegar before I'm going to give it a shot. Maybe I shouldn't be able to blow air through the pump while this brass piece is inserted so if you have any thoughts on what it should or shouldn't do feel free to tell me I'm barking up the wrong tree
I tore apart a spare pump tonight to re-familiarize myself with the insides.