Originally Posted by wegchef
It's a off white powder looking substance. I think I've read somewhere it's left over yeast matter.
It's actually not yeast, but beer stone. It's proteins from the beer that end up sticking inside the tubing. Even filtered beers (i.e., no yeast) have the same issue with beer stone buildup. BLC is formulated to break it down and clear it out. I've had no issue using BLC every month or so to clean my lines. I also see no need to sanitize them, but YMMV.