I second the water drop trick. Before I started steam cleaning tile and grout, I used to use washing soda and oxygen bleach on tile. It works great as long as you don't make it too strong. If you put too much powder in the water, it will leave a visible residue. It doesn't take much. I always used very, very, hot water, which I think did as much as the detergents themselves. I think most tile is not sealed, because installers never seal it, as far as I am aware. It's something tile cleaning specialists and home owners do later on. I'm guessing more people than not have never had their grout professionally cleaned, so it's not sealed either.
I suggest getting on a builders/contractors forum and asking their advice.
I know I probably beat this piece of advice to death, but seriously nothing works like a good steam machine on tile. It's a pain to lug it around from job to job, but it's so effective that it's worth it to me.
Last edited by Green Valley Cleaning; 04-05-2011 at 10:45 AM.