help setup new 180

[StephenHV]

I am about to get the following tank but am not sure what all the holes are for. This would be my first drilled tank and the question i have is the two holes, one at each end of the tank. Any ideas on how this would be use?

 

[worm5406]

Looks like for a closed loop system or even just extra return flow.

Would help to see what is inside the overflow box or even a bottom shot.