The overflow system on my 125g FW
is very similar to the one in picture on first photo. The trick is to build the overflow pipe as long as you can, so that it barely fits into the tank and the pvc
runs the entire height of the tank, this ensures that the water has enough momentum to force it and the air through the overflow system.
Another issue to be concerned with is how you prime the overflow. what I did was fill up the intake side and the vent side, while a ball valve after the who system kept water from flowing to the sump. Then I pressured the vent side with water to force all the air out of the overflow through the intake in the tank.
Another issue I had, was for the first month or so of use, the pipes syphon would need to be "restarted" Which I did by closing a ball valve just before the sump which would fill the pipes completely with water and release all of the air bubbles, then by opening the valve quickly, it would re-prime the system.
However, after about a month the pipes became coated with beneficial algae and slime, I'm not sure exactly how, but I think due to this "break-in" the pvc
overflow works perfectly, I never have to re-prime it and it no longer makes any noise.