drilling a set up tank.....

[digitalsteve]

how hard would it be to drill a tank that already has livestock in it , is there a way to do it without breaking it down , what if i transfer my livestock to a rubbermaid cont or something whilst i drill the tank. tank is a 20 g and i want to plumb a sump with some adequate flow but all the overflow boxes seem to be huge and take up space and that is the whole reason i am doing this . to eliminte unsightly objects in my tank ie skimmer and such . so as per my question is there a way to do this or do i have to break my tank down completely?