Clean tile grout can be achieved by sealing the grout so dirt and stains are repelled. You must wait 30 days after the tile is installed in order to seal the grout even with professional installation. There are two main types of sealant: Topical sealers and chemical penetrating sealers.
Topical sealants are easy to apply and sit on the surface of the grout, but need to be repeated every one to two years. Chemically penetrating sealers are more involved due to chemically bonding to the grout itself. If cleaned properly they can last up to two years.