I keep banging on about this, but why have an 18ft pole, I take you are having 3 x 6ft?
Why not try a 4 x 4ft pole, it will make your life so much easier, you can reach everything on domestic except 3rd storey, which an 18ft won't reach either, and when you close it down it is so much easier to handle and work on ground floor windows.
Granted, it does tend to whip at the joints when fully extended, but the sections dont bend.
Marc