How to get your old dirty grout looking like new again

Go from this

grout before

to this

grout after

Grout renewI have tried many things to clean the grout but it never comes clean and bright. Then I heard about this product called Poly Blend Grout renewal. It’s actually a colorant. To put it on they recommend a toothbrush and then use a slightly damp cloth to wipe off any excess as you go. You can buy it at Home Depot or on