If the weatherstripping doesn't do the trick, use a smoke stick (a lit cigarette if you are a smoker) and see if you can detect the leak around the base or top or inlet. You may have a leaky barrel and if that is the case, I'd suggest using a full lid plastic barrel instead. I've found some through local salvage places that were used for shipping food (e.g., tomato sauce or cooking oil) or detergents. I've gotten them for $10 and they are made from heavy polyethylene and a solid MDF or plywood top with a routed groove and weatherstripping will provide a better leak proof bin.