Could someone explain exactly why this discharge system works or what I need to do to fix it? I installed a backup sump pump last month. I noticed that the discharge pipe going through the wall was loose. Like really loose, like it wasn't even attached to anything on the other side of the wall. The pump was turning on once or twice an hour all month while it dealt with the spring thaw. But yesterday, a puddle of water appeard on the floor. I pulled apart the wall and saw water dripping behind the vapour barrier through the insulation. When I moved the insualtion I saw the pictured setup with the pipe sitting loose inside a much bigger pipe. I pushed the pipe in further and there hasn't been any more leaking. It looked like the bottom gap between the two pipes may have been taped at some point.
Since the 3" pipe is flush with the foundation, I can't add a reducer to connect the pipe properly.
Chisel out a half an inch around it so you can get a rubber repair reducing coupling on there.