What is the best way to clean grout between flor tiles?

Baking soda and vinegar paste, apply, let set a few minutes and scrub

I would probably mask the tiles and Paint the Grout

I have used simple green and a scrub brush. I do dilute the simple green with water. After I have scrubbed all of the grout I then go over with a mop and clean water.

If your grout is white, I use Great Valve's general purpose spray cleaner with bleach, then scrub with brush, let sit a while, then dry or mop with water.

I've used everything from professional cleaners, bleach, to homemade mixtures. If your grout was sealed, that can actually attract the dirt so even when you clean it, it will get dirty again quickly. I did find that peroxide and baking soda seem to work really well. I just cover the grout with baking soda and then spray peroxide over it and soak it. Let it set for about 30 minutes. I make sure it stays wet. Then....I use a wire brush and brush the lines. Time consuming but seems to work.

They don't tell you those things. It's like carpet cleaners don't tell you that putting soap type cleaners on your carpet actually attract the dirt faster than just using hot water.