Modifying an existing overflow.

[reddead38]

So I have an plumbed box in my 210 that is currently set up for a cannister filter 1 input 1 output no water in the box. I'm going to modify the box to work like a true overflow for a sump. This is what I have. so I have a 1/2" on the left I'll use for the pump return.
A 3/4" in the center about 12" down I'll use as a drain since using it like an overflow would be catastrophic if the power went out,
And a 1" on the right that has a pipe that hasn't been cut low enough to use as an overflow.

I plan on cutting the pvc down about 6" then drilling holes into the box about 2" from the top so it will overflow.

Does this sound like it will work or am I missing anything?

 

[reddead38]

Nobody?

 

[DN328]

red, I'd suggest you read up on Herbie drain. You will be able to possibly use two of the drains for that and the third if you wanted coming back through the overflow. Are the holes in your sketch on the side of the tank? How big is your tank? I ask since you'll want to make sure the pipe size and support the water volume you need.