I used to work in the motel business and we used straight liquid dish soap and small brushes to clean the grout in the shower as well as the floors. It works like a charm on almost anything like that, but needs lots of rinsing. Vinegar could probably be used as long as it was rinsed right away because it doesn't eat anything immediately, as it's a mild acid as far as acids go. Still, I probably wouldn't advise anyone to use it, as in this case, I doubt it would do as good a job as dish soap. Bleach would be dangerous to the user as well, I'd think.