How to clean grout between floor tiles

A friend of mine asked what to use for cleaning the grout between tiles. The thing about grout is that it's porous, so dirt gets inside the rough surface. The best answer is probably this one - don't let it get dirty in the first place! But that doesn't help if it's already too late. Just to illustrate the problem, I put wax crayon on a plate, and I can wipe it off fairly easily, but if I put wax crayon on a brick, it can't be cleaned off so easily. No amount of scrubbing is going to remove the wax that's actually stuck there inside the surface.

The WikiHow page almost gets there by suggesting a steam cleaner, but doesn't show the right kind, or how to do it. This is the type of steam cleaner I use, it produces a jet of steam that can blow dirt away.

It does help to use a cleaning solution on the grout to soften and loosen the dirt, but the important thing is to physically remove that dirt once it's loosened. Even using a paper towel or sponge will help to draw the dirt out. It doesn't look like it's working too well at first, because the dampness darkens it a little, but when it dries out, it's clear that the dirt has been removed.

So soften the dirt with a bathroom cleaner of some kind, and blow the dirt away with a jet of steam. It works for me!