If you dont want to use a hanheld grout scraper then use a 4" grinder with a diamond wheel to cut along the grout lines . Never use a hammer until the grout lines have been cut to keep surrounding tile from cracking. Dremel has a grout removal bit that doesn't work b/c the bit get dull after the first tile. It works well if the grout hasn't fully cured and your not happy with the color or bad hazzing occurs. Scraping grout is laborious work done by hand, and it is dusty when using a grinder so use a wet sponge against the blade when cutting the lines.
Brent hawkins of S.C.