Here's the dealio with mysterious leaks on the sides of Fluval canisters near the lift locks: often times water will find its way into the channel where the motorhead seal seats when the motorhead is placed on the canister. When the lift locks are engaged, the motorhead seal presses down into that groove and that water has to be displaced, otherwise the head will not seat properly. So, knowing this, the Fluval folks designed the canister with four small strategically placed holes to drain that trapped water. If you look at the undersides of the canister where the lift locks engage you will see a small hole on each side, or 2 holes on each latch. That is where the water is "leaking” from. Once the water is out of that internal channel, the leaking will stop.