So, this is my little 25 gallon Tru-Vu, as it came to me used.

I see the overflow to the right, and the center is where the wet/dry is supposed to go (were I using one). Now, how do I do the return hole on the left? Do I use a pump? A powerhead? Bulkhead fittings?
I'm really not this stupid on most things, but the plumbing part just confuses me.
I could also really use help figuring out what sort of water flow I should be looking for or what size pump/powerhead... and is that going to provide enough circulation, even in that small a tank, or should I mount other powerheads?
Please feel free to ask my any pertinent questions, and I apologize for the perspective horrors in the drawing
Thanks in advance,
Heidi, whose brain seems to be plumbing-proof past changing washers on a sink