You can use any sanded or non-sanded grout or a sanded or non-sanded grout caulking that best matches your tiles existing grout color. You can find these products at Lowe's or Home Depot in the tile section. I personally like using the grout caulking for ease of use, put it in a caulk gun and go. Whatever you decide to use make sure you read the instructions on clean-up and how long you should wait for the product to dry before getting it wet.