post pump just means the venturi(the air injector) is after the pump outlet,
asperating venturi means a venturi that feeds both air and water into the pumps inlet, where the impeller, a pinwheel, chops the air into fine bubbles, so a mix of air and water comes out of the pump outlet..
i was actually looking for the diameter of the tube that is used for the neck, but im going to guess that it's 2"
based on your other measurements...
so, that limits you to about 300lph of air injection...
allright, before we venture any further, i must enquire what size tank this is going on, because this is turning out to be about the same power of skimmer as i have on my 20g, and because of the shi*ty design of the posideon skimmer, it's not even anywhere as close as good... so ultimately because of the design, you might be better off putting your money elsewhere.