Drilling tank

[C&C]

I am planning the overflows, one on each side in the bottom.

I am also looking for info on how to make the overflows and the stand pipes. (Sizes would help).

As far as the return I'm not sure if I want to drill the back of the tank, I am somewhat worried about how to stop siphining during a power outage?

Any ideas comments would be appreciated.

Thanks
Chris