Originally Posted by Godfrey
Does your out flow from pump run up thru the over flow if so you could use that hole as an additional out flow by putting a tee in and plumbing it in with a bulkhead fitting
That could make back siphon issues. I know their are ways around that but beginners can get over their heads pretty fast. Sealing it up or putting a bulkhead and a plug are the safest options. Doing that, then plumbing the tank as it was designed to be, is the way to go.
Having said that, this setup is a pretty sweet find. There are lots of things a tank this nice could be used for. If it's going to be saltwater then getting a good book is the best first step you can take. There are a lot of tank, filtration and pluming parts that are explained, with photos, in any decent aquarium guide. We'll still answer questions and problem solve right here. The thing is, saltwater is expensive. The cost of a book or two is cheaper than just about anything else.