How do I clean the polishing powder out of the grout lines on a marble floor?

During the polishing try to keep the floor as wet as possible. Try to prevent the polishing powder from drying in the grout lines. While the floor is still wet apply a solution of stone soap and water, agitate the grout lines with the mop and pick up with a wet vacuum. Rinse the floor again with the stone soap and water. This technique should remove most of the powder residue.
TIP A soft deck brush or a soft brush on your polishing machine can also be used to clean the powder out of the grout. If you use this procedure be sure to use plenty of water.