Still deciding between an external or internal overflow for the future 120g upgrade. Starting to think I might now go with an internal overflow even though I prefer external so that you have more tank space. But the reason I'm starting to think about an internal overflow is because I plan on putting the tank up against a wall and if I have an external overflow, it will protrude out of the back of the tank and might not look as good since there will be a larger gap between the tank and the wall in addition to the plumbing being exposed. Still have to do some more thinking about it... Anyway, if I go with an internal overflow, what depth (front to back) do people normally go with? I'm planning to have 3 holes for 3 standpipes (2 holes for the herbie style overflow and the 3rd hole for an emergency standpipe). Not sure how big the holes should be for a 120g tank yet. But what's the narrowest dimensions I can get away with so that I use as little space as possible while still being able to work with the standpipes if I need to?