Air in Overflow box/Sump Feed (Issue)

I'm currently in the process of building a 92 gallon corner. Yesterday I plumbed and built a 20 gallon sump/refugium. I'm using a Eshoppes PF800 800gph overflow box with a 700gph Pondmaster pump. As soon as I started the overflow and pump, there's constant air blowing out of the pvc leading from the overflow box into the sump. Any ideas what may cause this? I'm using 3/4" pvc. It appears if I added a second siphon hose, it may cure this issue. The overflow box doesn't appear to maintain enough water in it causing the gargling noise. Should I add a ball valve somewhere? Any assistance is appreciated.

Video here: (EDIT)

http://vids.myspace.com/index.cfm?fuseaction=vids.individual&videoid=105540123

http://vids.myspace.com/index.cfm?fuseaction=vids.individual&videoid=105540121

Here's some photos:

 

Definitely not a ball valve issue.

I think this issue is fixed with some airline tubing, run back up the drain line. I'll wait for someone else to comment more though.

 

http://www.3reef.com/forums/general-reef-topics/overflow-silencer-quick-question-86048.html

http://www.3reef.com/forums/i-made/herbie-overflow-video-79073.html

 

As you can see, I tossed a siphoning hose into the overflow box just to see what it would do and it made a tremendous difference. Although, it's still not correct and making some gargling/bubbling noises. The video isn't really the same situation.

 

Should I add a ball valve to slow down the exiting of the water from the overflow box?

 

No, never do this. You're setting yourself up for a flood with that idea.

 

I think a larger drain line than 3/4" on the over flow would probably help out . the shot of the tank looks like the water level is higher then the over flow box ??? is the return pump moving more water than the over flow is draining?? a larger drain on the over flow could help there to or a ball valve on the return from the pump.

 

IMO you don't have enough flow thru your display. And no matter what you do the drain line is always going to pull air down with it. I'm curious as to why you reduced the plumbing from the bulkhead by 1/4"?

 

Here's 2 videos.

92 Gallon 1, Overflow noise.

92 Gallon 2, Overflow noise.

 

It sounds like a toilet flushing. Check the video.