use at your own risk, but at one point on my old 33g which was in a bay window I had a 15g on milk crates behind it fed with a small powerhead with a larger diameter vynil hose contraption siphon feeding back to the tank. the refugiem sat a couple inches higher than the top of the tank but the water levels were about the same. I used a toms aqua lifter to ensure the siphon was maintained in the hose.
worked well for a couple months until I cracked the refugieum leaning on it<nothing else to lean on back there>
Other than that hole saws are cheap and probably whatever plumbing is done properly is more safe
