There is some sort of horrible smelling cleaner that supposedly removes grout for situations like this. I don't know the name, just that it stunk up the whole house for days after our tile guy used it on our decorative tile. It didn't remove it all, but it helped. Don't know if he didn't spend enough time or if the grout was just that hard to remove. I also didn't understand how it was going to work on the grout embedded in the decorative tile nooks & crannies, but it wouldn't hurt the grout in between the tiles.

One thing to consider is the potential difficulty of cleaning those nooks and crannies in a shower if they aren't filled.

mydreamhome-- most likely it was muriatic acid, and that's the WORST thing you could use. The fumes alone are enough to ruin bright metal finishes, as well as hurt the respiratory systems of small anumals, and in stronger quantities, even humans. That's some dangerous stuff to use in a home, and in fact it's now recommended throughoutn the industry that it not be used on tile and grout AT ALL any more.

Lynnblack's post was my next point. If you don't fill them with grout, they'll fill on their own with some real nasty stuff later.

oh what a shame:(