I have done this numerous times with a DIY setup that works great and is much simpler and more fool proof than the one referrenced in Jared's post. From the picture, I'd say that sump comes too close to overflowing when the power cuts off. And the sump does not have to have those baffles and if his "weir" stops flowing while the power is on he will overflow his main tank.
I don't know how to add the image. When I click the image button it asks me for a web address! If you email me I'll describe how it's done and send the drawing.
Mark [email protected]