External Overflow

[Ryan]

Ok so I am looking at buying a tank that has been build already without an overflow box. The tank is 20 x 20 x 24 and I dont want to cut into the footprint with an internal overflow.

I want to run a Herbie overflow on this tank with a single 1/2" return line then use my Koralia's for water movement. So I know how to build an external overflow but my question is how do you go about cutting a notch out of the glass big enough for the water to spill over? There is only going to be at most 450 GPH (thats what the flow at the head is rated for on this pump so it wont even be close). I was hoping to be able to get away with a notch 2" deep and 6" long even 4 would be great.

My other thought was drilling the tank near the top and running a coast to coast but only going down the tank 6 inches or so.