I bought the 4" brush for the pellet stove pipe and the flexible rods. I could not for the life of me get the brush to go past the first 90 elbow. I wound up disassembling the whole flu system (10 feet and maybe 5 joints plus the tee at the bottom), what a mess, but it's clean now. What do you guys do use to get the brushes to go thru the piping? bjr