I dont have an internal overflow so i am assuming that is the problem. I have a elbow pointed towards the top of the tank with a strainer on it. I had an overflow box but it wasnt working, so i removed it about a week or so ago. The reason it wasnt working was because it had a crack in the side of it. So i was think i could take a fairly large cup and cut it in half, dremel out the top of it and set it over the drainage elbow. Would this work? Or are there better options out there? Please take into consideration that my tank already is stocked with 70lbs of LR, 5 fish, 20 inverts, and at least 15 various types of coral. So more than likely i cannot drain the tank.