Stockman Overflow Problem

[dbg]

I have a stockman overflow installed in an Eshopps 800 overflow box which drains into my sump. My return pump is a magdrive7 with gate valve. The whole system is 1' PVC. I have to restrict the flow of my mag7 to match the drainage of the overflow. Recently, I was messing with the stockman and realized that covering the airline tubing in top with my thumb makes the flow go much faster. When I do this, I no longer have to restrict the flow on my mag7 (but, I would have to deal with the loud gurgling from the plugged airline in the stockman).

Anybody know of a way to increase the flow of an Eshopps 800 overflow box? I'm tired of having to restrict the flow on my magdrive pump (I want the extra circulation in the tank), AND the overflow can clearly handle it since covering the airline on the stockman allows so much more flow. Why does the silencing part of the stockman slow the flow down?

 

[Reefing Madness]

Return pumps aren't meant to be used as flow in your tank, they are just there to return water from the sump. If you need more flow, get more power heads in there. I wouldn't mess with the overflow.

 

[dbg]

I suppose I'm more curious why covering the airtube in the cap of the stockman increases the flow so much. I have read of other people having this same issue; something about the airline tubing in the top of the stockman creating a siphon. It seems that some folks have drilled multiple holes in the cap of their stockman, or increased the diameter of the pipe running from overflow to sump, but I haven't found a definitive answer on trouble shooting the stockman.