So how do you cut the bad grout out?. Box knife, many areas were filled with this crap..
Do you have to color-seal the whole area of that particular tile in order to get a match on the grout, or just the area you repair? SGA fortified sanded grout
Unsanded grout on walls and back-splashes? Unsanded to fill hairlines (that I'll carefully open a bit, sanded on everything else.
I've used chisels when lots or all of the area need to come out, lightly tapping. There is a nice grout drill bit for a dremel tool that works well close to tiles. It's not super fast, but can work.
This kind of work I'm way tooooo slow at. I get all OCD in the head and will work way to long trying to get all the grout out when it might not be necessary.