With such a large piece, are you sure it isn't just loose lint? Some flannel is VERY linty, the first several times it's washed. When I wash a piece of several yards, I wash/dry, then take it outside and give it a good shaking. Then I wash/dry it again. During each drying session, I clean the lint filter, about every 10 minutes. Doing an entire bolt of flannel . . . well, I can't even imagine how much lint must end up in the dryer!!!