When I think of creosote I think of a sticky gew but I've never actually seen it, I think anyways..... See, the junk I clean from the walls of my piping is more like soot to me. Messy, black powdery stuff about 1/4" thick and that's after a whole long cold winter in the north but I only burned about 3 1/2 cord last year. On my inside double wall pipes I take them apart and bring them outside and to really clean them well I use a pressure washer. It cleans the walls better than just a 6" pipe brush and and hose end sprayer. The way I figure it is since I cut the air supply there is going to be soot. That's the way it was when I ran boilers in schools. Not enough air meant more soot to clean from the tubes. T minus 5 weeks until heating season up here!