IMO: An overflow box is a bad idea. It cannot give you a 100% operation guarantee which is needed otherwise if the overflow stops for whatever reason (Usually after a power failure) and the siphon doesn't start back up then all the water in the sump will be pumped out into the tank. This will most likely cause a minor flood.Now I know people who swear by these things and have never had a problem. But, that's just not how I do things. I like to be able to say there is absolutly no way my tanks can flood, Because it was designed right from the begining.