Synergy Shadow overflow , U fitting question

[125mph]

I just got the overflow. It includes two "U" fittings. Both have holes in the center for air. I thought only one was suppose to have the hole while other should have no hole to create full siphon?


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[minus9]

https://www.youtube.com/watch?v=vXIllsPD8-w

 

[WWIII]

I have mine setup for full sypon with no elbow. Then the trickle and dry emergency use the elbows.

Also, if you haven't already, use clear medium pvc cement on the bottom to connect to plumbing. I used the abs transition cement the first time and it made a reaction that cracked the box in 2 spots. The clear medium cement has worked perfect for past month.