Grout Stain
If the grout around your tile is stained and dirty, but you don't feel like digging it out to replace it, consider applying a stain.
How to Stain
First, clean the grout with tri-sodium phosphate. Apply and scrub with a small, brass grout brush.
Rinse the grout after cleaning and allow it to dry overnight. Then apply the stain.
-- Tips courtesy of HomeAdvisor.com