I have a tumble dryer in the utility room with a hole in the wall (former cat flap) nearby. I have fitted (rectangular profile) ducting behind the tumble dryer, through into the cupboard next to it and out through the cat flap. i have filled and plastered around the hole. the problem I now have is that condensation runs off the ducting and fills the cupboard with water. How can I avoid this? Do I need to seal the joins in the ducting with tape, or do I need to insulate the ducting? If the latter what should I use to insulate with? Thanks