As an alternative, check out the CPR CS (continuous siphon) series of overflow boxes. It has a built in siphon that can be adjusted with screws to set the water level in your tank (no u-tube to mess with). You can also purchase an aqua lifter pump that quickly and easily attaches to the top of the siphon to prevent any siphon breaks. Even if the power goes out and the siphon breaks, when the power comes back on the pump quickly sucks the air out of the top and you're back in business. As an additional plus, you don't have a large box hanging there on the inside of your display tank. In the sump, you can position the return pump high up near the max water level (with suction cups or some other means). That will work as a fail safe...that way, if the siphon were to break during an electrical outage and the aqualifter pump were to fail at the same time, the return pump is limited to how much water it could pump back into the display tank. The worst that would happen is you could lose your return pump if it runs dry too long. I'd rather this happen than a flood. Also, be sure to place the outlet of your return line high enough in the display tank to prevent a large volume of siphoning back into the sump if your return pump were to fail. That way your sump won't overflow. I have this set-up on my 72 gal
bowfront and it works perfectly every day. Best of luck to you.