to get rid of the nasty black gunk in your drain: 1. Boil a pot of water. 2. Meanwhile pour baking soda down the drain. 3. Once the water has reached a rolling boil pour it down the drain. 4. Let the water and baking soda work at decomposing and sterilizing the grime for 10 minutes. 5. After 10 minutes, pour 1 cup of bleach down the drain to completely kill any remaining mildew or bacteria. this process every few months. It will also keep the nasty mildew smell at bay.
How to Clean a Tub - "So I cleaned my tub as I would normally would. Then I cleaned it as directed on this site and wow I could still see all the grime come off as I cleaned it this way. I know how to clean my tub now! Stocking up on vinegar (and not just for salads and pickles)!"
ONLY use this and it leaves floor spotless. (Heavy duty floor cleaner recipe: ¼ cup white vinegar 1 tablespoon liquid dish soap ¼ cup baking soda 2 gallons tap water, very warm.) It leaves everything smelling amazing.