Need some help with my sump overflow/return for my first time with sump

[spitz006]

I have a used 90 gallon aquarium with two holes drilled in it and a sump that’s probably 30 or 40 gallons. I bought a bunch of stuff and pvc and dicked around, I’ve now got bulkheads on both the holes, I bought a big dc pump, and everything underneath the tank is pretty much done. What I’m still stuck on is at the top of the tank. How far below the return should I cut the overflow to be? A couple inches? And what should I do for the return, buy a “T” and a little 1/2 pipe to fit in those grooves and a couple nozzles?

 

[BIG-G]

You probably want to set the overflow just below the level of the weir slots.
Just in case the shroud ever leaks it won’t drain the tank, it will also help keep it more quiet because the water won’t have far to fall.
The return will need to be at water level to stop the tank from draining during power outage or return pump failure.
The other option would be to drill a small vent hole in the return line just at water level to break the siphon for the same reason.

 

[BIG-G]

Depending on the situation another option may be to have the return come over the side and set both bulkhead as a herbie style overflow with one drain being a full siphon and the other an emergency drain.
The full siphon would be just below the slot level and the E-drain just at the top of the slots but low enough that the tank would not overflow.

 

[BIG-G]

Correction: for the herbie you will want the full siphon lower then the slots to maintain the full siphon and the E-drain just below or at slot level to take up the rest.