Sprinkle baking soda over the grout lines as if you are sprinkling powdered sugar over a cake.

Combine 3 cups water with 1/2 cup Castile soap in a mason jar or glass dispenser. Shake gently to combine, but not hard enough to create bubbles.

Drizzle the diluted Castile soap over the areas of the tile covered in baking soda (as if you are drizzling a scone with glaze).

Scour the dirty grout with a coarse bristle brush using quite a bit of elbow grease. You may need to repeat scrubbing a few times over especially dirty areas. You should see the baking soda and Castile soap reacting as if to form a thick paste. If the paste dries out or becomes too thick, just add a little water over the top and repeat the scrubbing process.

Remove the paste residue by wiping up the freshly cleaned tile area with a wet rag. You will find that it takes a few rinses before the paste is gone, but do so quickly so that the dirty residue doesn’t dry into the tile. If you notice a build-up that cannot be removed with water, wait until the area is completely dry, then rinse with a diluted water:vinegar solution (about 1/2 cup vinegar in a few cups water).