100 Gallon

[Kjay]

I have 100 gallon tank. It has corner over flow box. In it there are 2 holes drilled both accommodate 1 inch bulk heads.
Should I use it for 2 drains or one as drain one as return

 

[Kjay]

Sorry edited to make more sense

 

[EricTMah]

Go two drains and return over the top.
If you go one drain and it plugs. You're pooched

Sony Xperia Z3

 

[TORX]

Over the top return. 2 drains, one full and other trickle/emergency. With a gate valve on the full siphon.

 

[Kjay]

Much appreciated