This is my go-to method for restoring dirty, old, tile grout. It is a serious clean that goes beyond your basic everyday products.
-------Products That I Used (Folks, these are the affiliates!)-----
Tile Grout Restorer - https://amzn.to/3dnPpJj
Rubber Gloves - https://amzn.to/2W8Cjtw
Knee Pads - https://amzn.to/3cbbNWd
Sealants that I like to use:
( Penetrator) 511 Impregnator - https://amzn.to/3k5wczm
or Stonetech's Grout sealer - https://amzn.to/3m2u11k
( Surface/Enhance) 511 Seal & Enhance - https://amzn.to/3m7qJtR
or Stonetech's High Gloss - https://amzn.to/32dzASO