Here’s what you’ll need:
First, scrub the grout thoroughly with a grout scrub brush (seen in picture) and water. I actually use a water/oxi-clean solution to brighten the grout a bit (let the mixture sit on the grout for a little while to brighten it then scrub), but you could also use baking soda. Make sure to wash off afterwards. Then, let dry for at least 24 hours.
Then, pour some sealer into the Grout Sealer Roller Applicator and roll on the grout. I had to gently squeeze the bottle a little at times b/c I couldn’t tell if the stuff was coming out or to get a little more to come out, but it worked really well and the sealer stayed mostly between the lines. If it gets on the tile, just wipe it off with a damp rag. Let dry as per directions on the bottle.
Hopefully, this sealer will help keep the grout from getting stained. We shall see.