The intake tube on the suction side of the sump is what is causing you to have to top it off daily. I understand your logic behind it, if you lose the siphon on the U-Tube your pump would overflow your DT. But have you ever lost your U-tube siphon? If you design it right, you should never lose it unless someone pulls the tube out, the water levels in the overflow buckets on either side should stay at the minimum should the tank level lower, etc. Your DT water level remains where it is at all times because of the overflow level, and your sump will lower due to evap. What I would do is lower your overflow buckets in the DT so that the water level is a little lower, then remove the intake tube on the suction side of the pump, and lower the level of the sump (or raise the pump). Then test your setup by purposely pulling the U-tube and make sure that the pump doesn't overflow your DT. Then set it all up again and turn the pump off to make sure your sump doesn't overflow due to backflow through the pump. If it's designed right, you should not have to worry about overflow of either tank. If not, it's a disaster waiting to happen.