Air intake for my overflow

I have a question about my overflow.  It is just an ABS street L glued through the back to another regular L to make an S shape.  Right now it has to suck air in at the water level, which is fine, but I would like to add more flow.  I am concerned that if I add more flow it will not be able to suck enough air and will overflow the tank.  I have room directly over the street L that is inside the tank to drill a hole for a breather tube.  My question is how does the breather tube affect the water level, and if I put a breather tube in will it allow me to run more water?

Thanks,
Fax

I cannot change the design.  It is kinda like this, with the tank going between the parenthesis.  If you tilt your head 45 degrees to the right it is just right.  I will take a pic when I get to the office in a bit.

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Fax

It could also be done by drilling a hole in the top of the outside elbow and glueing (silicone?) a length of tubing with an adjustable valve to allow just the right amount of air to go down. Note, that the end of the tubing must be positioned above the tank water level.

The durso principle, if one may call it that, actually allows more water to fall down the overflow pipe.

Amazing...the technology exists, all one need do is ask!

Edited by Mark Peterson

The durso design can drain a tremendous amount of water and have silent operation.  As an example (I'll make it short and leave out most of the part where I was LAZY ):  I have two (1 inch) overflows in my tank.  Last month I noticed that the water level in the tank was a tad high (normally it's only about 1/8" higher then the overflow weir).  I found that one overflow was completely plugged off with algae (mostly that really small bubble sized valonia) and the other was mostly open.  Well I was busy with something else and didn't do anything about it.  Over the past weekend I noticed a little bit of water along the bottom brace of the tank.  The water level had risen to the point that water was slowly leaking out of a poorly siliconed top brace.  I was about 1/4" from overflowing my tank .  The one remaining overflow was restricted to a hole about the size of a nickel and the durso was still more or less working (my return pump is a Velocity T4, 1400 gph).  That's a lot of water to drain down a hole that small.  Anyway, sorry for the diversion, back to your questions.

So what is the critical element?

Durso's work so well because they are essentially a controlled siphon.  Your drain is open in the tank so can not be "dursofied" and will be very difficult to quiet, imo.  The concept is simple, but much easier to explain in conversation (mainly because I don't have time to write it all down).

Ok...  It'll work as you have it.  The level will increase (you won't know how much until you try it).  It'll be slurpy and gurgly through.