Here is my undrilled sump. My tank has been running for 11 months with a CPR overflow, and have never had any problems, even with power outages. I use a maxijet powerhead hooked up to the overflow via the venturi air hose. Its attached to the air release nipple on the top of the overflow. I also have a check valve on my return line from the sump to prevent back siphon into the sump in case of power outate. Also return line has a few holes drilled 3/4" below water level in the tank as a back up in case the check valve fails.
