What are you having a problem with? Those overflow boxes can be a pita to get started. What I like to do is fill both sides of the box with water, then dunk the u tube in the tank and hold it underwater upside down ( so the ends are facing up). Cut the fingers off of a rubber glove (if you have an imagination, you can use other things for this...just make sure they are...ummm...untreated) and slip them over the ends of the tube to seal it. Take it out of the water and put it in the overflow. Now, with both ends underwater, slip the rubber fingers off of the tube. If you did it right, there will be no air in the tube, and the overflow should flow when you fire up the system.