Gurgling noise in overflow box (the air intake hole of pipe # 2) -diagram included

They told me to use a ball valve at Aquatic Dreams :: Your Saltwater and Reef Aquarium Specialists Clearfield, Utah This is what they use on their tanks in the store. They have no problems with it and neither have I. Also My tank is now quiet as can be

 

Glad you reached your goal.

I was merely pointing out that if you reduce or regulate the speed of the return
TO the sump, often times the Return pump will overcome the capacity of the return to the sump, and it overflows your Display tank, making for a wet floor, etc., etc.

That's all I was saying- just saying ;-)

 

What if the valves all the way open and the return pump is still slurping?