Fill the marble tub with warm water. Pour 3 tbsp. of dishwasher detergent into the water while the tub is filling up.
Add 1/2 cup of bleach to the water once the tub is filled. Do not get the bleach on sidewalls or tub deck.
Scrub the tub with a soft brush to remove dirt and grime. Once you are finished cleaning the tub, drain out the water.
Refill the tub again with warm water to thoroughly rinse out the soap, bleach and grime. Drain the water out of the tub.
Wipe the excess water from the tub with a thick towel. Inspect the tub for remaining dirt and grime. If the tub is still dirty, repeat the entire process.