First you have to find out if you can drill the bottom of the tank. If the glass on bottom is tempered than you can't drill. A good compromise between drilling the bottom of tank and a hob overflow box is to drill the top side of tank, then put in a overflowbox inside the tank that empties out through the wall. If for some reason the drilled hole starts leaking there is far less water on the side of tank than from the bottom. Even with a hob overflow box you can set it up so the tank won't flood if you lose siphon. The trick is to make the return chamber small enough that all the water will fit in the DT. The next trick is that the sump holds enough water for when the power goes out and the DT drains down. The third trick is to never ever rely on check valves to prevent a flood. Check valves will fail - always build with siphon stops in place (holes drilled into the correct location can do it). And lastly, test your sump for pawer failure and make sure it cannot flood.
