How Can I Clean White Tile Grout On Floors?

I also have sand grout.  I was told you can't seal sand grout and I have tried to seal it and it didn't work.  Today there is sand grout that can be sealed on the market but not grout from 12 years ago.  Kaboom works well, although it still is a lot of work.  Spray it, leave it, scrub lightly, rinse.  Also if desperate, bleach and h2o mix.  Its not good to do this to much b/c it will eat at your tile but it will look like new for a while.

  Sanded grout is used for flooring because it is more durable. Unfortunately, it is porous and should be sealed when first applied to newly layed tile.
Since your grout was not sealed, it is unlikely that you will be able to get all the dust and dirt out, because it has absorbed into the grout.
 Not much can be done concerning this, except to regrout the floors and seal it once the grout has set up and hardened.
 You can purchase grout scraping tools at your local supply store, scrape the top layer and re-grout. It is a lot of work though.

I have used Oxy Clean with some success. I let it sit for about 2 hours before rinsing it off. But it does sound like it needs to be redone and sealed.

Use baking soda and vinegar mixed in a spray bottle, leave on there for a few minutes and wipe off with a rag, it should come out.

My uncle owns a tile & marble installation company in Florida.  He swears by vinegar and water.  Good luck!