How to remove grout not even a dremel will remove?

You can buy a little scraper tool that has a pointed or 'v'shaped end to clean the gap between the tiles without damaging them. after that its a matter of re-grouting. Make sure the area is dry first...

a screw driver and hammer-be careful not to scratch the tile or a chisel or putty knife and a hammer- test it out and see what works best for you- you can also just remove half of it and re caulk to...

My dad does tile and i help him out every once and a while with it.. and one time something similar to this happened and we had to get a chisel and hammer and scrape the mark out of the grout.. of...

You could try vinegar and a scrubbing pad, but there are commercial preparations available at home centers for this specific purpose.

If it is chunks you are referring to, a scraper or screwdriver will pop them up. If it is the haze or film after a fresh installation, hit it again with a sponge and clean water.