I drilled my at the bottom and used PVC stand tubes at opposite ends. I made the in flow as a PVC tee nearly as wide as the tank and drilled a series of holes so it shoots water along the surface. I placed the tank high enough it drains back to the main sump then I supply it with water from a second pump that drives it, my refugium, and reactors from my sump. With that being my first glass drill project I found it not nearly as difficult as it looks.
When I drilled, I first drilled a scrap piece of ceramic tile, then I used the drilled tile as a jig and duck taped it to the bottom of my tank (up side down) and kept a steady slow stream of water on the hole and took my time. Do not drill to close to an edge of the glass. Drills are easy to get for cheap of e-bay, I bought the cheapest and have no complaints.
