I have some one gallon jug from my second batch of brew. I cleaned with Oxyclean, the first jug came out sparkling like a Russian ballerina but the second one had a very very, faint, slight black lines at the bottom. It seems like a stain, or something because I've Oxycleaned it about 4 times and it still looks exactly the same. Obviously I want to make sure this isn't going to mess with a batch. I don't have a camera readily available and I don't think the camera would even be able to see it. I'm just not sure what it could be. If it were anything in the world I would assume it's some kind of resin. Could it be hop resin? I just don't know what it is because nothing seems to remove it (even overnight soaking). I can't imagine whatever is leaving that can't be good for my fermentables. Any ideas?