What an easy gig. First you Clean the Grout with Grout Cleaner. Then you get Ceramic tile Grout Caulking at HD. Match the color to the original grout You can put some of the Caulking in a cup and add some water. Make a paint out of it. Brush it into the grout and wipe with a sponge. Or you can just seal it with the Caulking and wipe with a sponge. House wife's love this deal and recommend it to all their friends. You will get plenty of work from this Service. Then you up sell from there.