newbie piping questions - what size return - what size overflow?

[Milad]

can I not use some sort of check vavle?
http://www.plastomatic.com/ckm.html

those holes are already drilled so thats why i figured ill use them.

Originally Posted by Mr OM

You might want to reconfigure the returns to the the tank, they are somewhat low, if the power fails you will have a flood on your hands, ideally they should return to the opposite end where they would move the surface water to the overflow box but that would alter the aesthetics of the tank. You could reduce the width of the overflow box and bring the returns up higher on the end sides to reduce the flooding issue.