When a keg kicks: If I have another keg carbonated and immediately ready to go, I simply install the new keg and start tapping it. If I don't have another immediately ready to go, I flush the line with warm water (using a pressurized plant mister modified with a ball-lock fitting), then let it sit until the next keg gets installed. I have never flushed/cleaned the lines, after ~4 years, with anything but warm water. I do inspect the lines closely once in a while, and so far no beer stone or mold or anything else. Beer always tastes great. Cleaning with BLC or whatever once in a while is probably a good thing to do, but I've never done it, and I'm still tasting great beer on tap. One factor, though, is probably how often the line sits empty and untapped. Mine rarely do. But if your tap line sits for a long time empty, not a bad idea to run BLC through it.