Ryan,
I disagree that the air is shoved out the end of larger pipes.
The suction part won't start until the air is out so that is a catch 22.
The 2" vent pipe on my ponds 12" pipe was set to low. The 12" pipe ran an awesome amount of water, but never a full pipe during a flood event where we had 20" of rain in 48 hrs or so. The pipe ran about 2/3 - 5/8 full on the discharge end while the pond was at spillway elevation. The 12" pipe had over 4' of head at that point. (about 8 psi)
