External overflow: pipe dimensions?

[Jessienzo]

Hello Nano Reefers!

 

I'm making an external overflow for my 18x18 cube, but I'm unsure of pipe dimensions. 

 

Was thinking about 1" between inside and outside box and 3/4" between outside box and sump OR 3/4" and 1/2". 

 

Also wondering if I should try to fit a beam animal setting or just go with a simple hole. 

 

Thanks for your advice. 

[Friendly]

I'm looking into something like this for a 5.5 gallon cylinder that's just shy of 12" in diameter and height.

 

a lot has to do with how much flow you need. an 18" cube is approximately 25 gallons and you should have 4 - 5x turnover an hour, so 100 - 125 gallons per hour.  this will have to be matched to your pump, which would tell you what diameter plumbing you should use by it's intake/outtake.