On my late 70's home, the clothes dryer exhaust vent transitions from round to rectangular inside the wall cavity then back to round at the top plate. Problem is that it's badly clogged with lint and I don't know how to clean it. I tried my 120 psi air compressor but it takes a brush to get it all off. I think it's a 39-year accumulation.
Any ideas? The only solution I can see is to run a new 4" round on the wall surface, but I'll have to penetrate several plywood layers on a wall cabinet before it arrives at the ceiling.