Suggestions and help with plumbing my tank please?

[Jason McK]

I think the best use of the lower hole would be for a closed loop. If you wanted to go that way. It could draw water through a pump then returned with plumbing over the top of the tank.

I would not recommend using it as a return. Power goes out and you'd have 120G on the floor.

I'm no expert in overflow design, typically I've always built a box. Untamed is the Herbie expert.

J