Not sure if this is helpful to anyone, but I killed a raccoon ( young boar) by mistake while draining a rain barrel for winter. I had opened the valve on the bottom, unaware that some local raccoons must have been using the barrel as a water source. The barrel would have been about 2/3 empty when a raccoon fell? in and drowned. I believe it happened while I was in the barn at dawn because the barrel was clear and full at that time and I found him about an hour and a half later but hadn'd heard anything or I would have assisted him. Perhaps the raccoon expected the water to be within inches of the top? I know that drowning traps are used for skunks, and that rain barrels can be dangerous for cats but I suppose there is a method here. I'm not experimenting, I've emptied the barrel for the winter and it's upside down now.