I couldn't find the post you are referring to, but there are some suggestions for you on this post from a few months ago:
Hi Carolyn, I think you were referring to this post, it's called Tile Guard: http://www.hometalk.com/546868/how-to-restore-grout-the-easy-way
If it is really dirty grout you can rent a Commerical steamer. I do this once a year then after it dries I re-seal mine several time.
That is really interesting! I was trying to find the same post, with no luck! I do not believe that zap was the product.