You mopped the whole floor. The tile looks fine. The grout lines still look gray, and you’re starting to wonder whether the only real answer is getting down on your knees with a toothbrush. It isn’t. The method that works best barely involves your arms at all. You soak the grout in oxygen bleach, walk away for twenty minutes, and wipe it up. The soak does the work you were about to do by hand. Here are four no-scrub methods, what each one actually fixes, and the popular tip that can quietly wear your grout down if you keep using…