Do a search; it's been discussed before. Ollyit did it recently on his 4m searider. It's a fairly easy job. All you need is a hole saw, a short length of plastic piping (drainpipe is good), a piece of hypalon, a tube of sikaflex and some cable ties. Drill the hole, glue the pipe in the hole with the sikaflex (possibly glass it in if your worried about water getting into the transom). Then glue your piece of hypalon into a tube, and attach to the drainpipe with cable ties. Chances are it will leak when the boat is a rest. If this is the case put an eyelet in the end of the trunk, and tie a rope from it to a small cleat inside the boat.