EllenG, it can very well be sludge but also disintegrated flukes and a number of other things. No flush is the same. Over the years I've eliminated matter of different colors, consistencies and with various odors. Very often it was brown sludge followed by green stool. Can't tell you if that's bile or not because my bile has never been green. However, the stones that come out are green so it could be mushed up cholesterol.