Dan and gaswizzard,
Ok, maybe I am an idiot and/ or a muppet. But the original posted question hasn't been answered by either of you - where & how to properly fit a booster pump in a gravity system?
Slating me is all well and good, and saying "If you knew how to install the pump correctly you wouldn't require a check valve on the open vent" is great, but what is the correct installation point? Where would you place it so that there would be no risk of air suction from the vent pipe? And, I still can't see why there is an issue fitting a check valve on a vent pipe- they don't require much pressure to open in the flow direction so it 'should' be safe. Unless I'm wrong.
I assumed that this forum existed for people to get help from other people, perhaps more experienced than themselves. Please enlighten me, and the original poster, of the correct way to fit a pump in this situation, and why a check valve on a vent is a bad thing! I don't want to plumb badly, and I'm sure you don't want to see people doing it either.