I have a couple questions conscerning an overflow box since i am about to construct a wet-dry filter out of a 20 gallon and wanted to avoid any drilling on the tank that i can. First off, is it possible to construct your own overflow box or do you need to buy them? If it is possible, how hard is it and what materials are we looking at? Cost of materials? Second, if you can not make your own and you have to buy, what is the cheapest choice? so far all of the ones i have come accross are at least 75$ which is a little bit to pricey in my view. Links and such would be appreciated here.