I have a dryer vent going through the attic and venting out the side wall. The attic is insulated to R40 and the pipe is insulated to R12. Rigid steel pipe was used(4 in) and there is one 45 elbow but I am getting water coming out the vent outside and back into the dryer. The total pipe run is 20ft. The outside vent is caulked and spray foamed. Any suggestions on how to eliminate this moisture problem.