I have about 14' of pipe total on my system. In over 35 years the system has never been cleaned. I installed it new. The house is 41 years old with out any problems. What makes you think any thing about creosote because you have water or moisture. I burn junk in my stove and I mean junk no creosote ever. I do not know how any system can have 18' feet of any thing. The previous AS members are on track as they described the problem. The fix not quite sure about, but there must be a solution with out rebuilding the house. It could be as simple as installing double wall or triple wall. To have a system to fight with takes all the fun out of sitting by the stove on a blustery day. Thanks