Just my opinion, The probe must be at all times covered with water. If I were to drill a hole thru the top of the tank and the water level droped it would expose the probe. If I were lucky the probe would shut down, if unlucky it would be permanent. I would drill a hole in the side of the tank, or in the filter box where it will always be below water level. This is only what I would do, if I were in the situation as you described it. ON the Ice Probe web site it says PROVIDED the ice probe is COMPLETLY submerged it can be install thru the top sides or bottom of any water resivoir. I hope this helps you Steve