Corner overflow question

[ynotme4886]

I was cleaning out the tank I just got and noticed that when I was draining the tank the water level partitioned off by the corner overflow was not draining. The front removable black faceplate has a grate like opening at the top and another grate like opening at the bottom. However the part that is permanently mounted into the corner of the tank has only an opening at the top for the top grate.

So by the way it is set up it looks like the water in the lower part of the partitioned section will stagnate because it has no way of ever returning back into the display part of the tank. The plumbing for the sump only drains off the top few inches of the overflow so it looks just like dead water in the lower part of the overflow.

I understand why the plumbing only takes the top few inches off of the overflow (power outage and tank would drain completely into sump/floor) But I dont understand why the bottom grate even exists on the removable part of the corner overflow. Personally It looks like a good place to drill a hole and put a powerhead so that the water in the bottom of the overflow can circulate and return back into the display part of the tank instead of just sitting there and not moving.

Anyone have any thoughts to help me understand how this works and why it is the way it is?

 

[Ligershark]

the middle and bottom slits in the overflow box "outer shell" do pull some water from the middle and bottom of your tank. that is the purpose of those slits in it. you just dont notice it as much because it is not as strong and you cant see it. all overflow boxes, mega-flow,aqueon, oceanic, perfecto, corner of whatever all work identically. believe it or not that stagnant water also has a little flow, you could even throw a back up heater or thermometer in there instead if your sump. if it was stagnant the temp would be off. mine isnt. that overflow box is basically a refugium.

 

[mikem]

The water in the bottom part does move.
When the water moves over the fixed part of the overflow on the top, it siphons the water from the lower part and pulls it up and over the top.