Dark stains can appear inside the bottom of a toilet bowl due to hard water or particles from your home's water supply. Toilet cleaning products placed inside the bowl's water may remove stains on the side of the bowl, but these products won't stop stains forming on the bottom of the bowl. Removing the water in the toilet bowl and using a homemade cleaner will remove stains and unpleasant smells.
Turn the shut-off valve found under or beside the toilet cistern clockwise until it will no longer turn. The toilet's water supply is now turned off.
Flush the toilet. Plunge the toilet's drain until there is no longer any water in the bowl.
Pour 125 ml (1/2 cup) of baking soda into the bottom of the toilet. Add 250 ml (1 cup) of undiluted white distilled vinegar into the bottom of the toilet vowl. Wait until the bubbling reaction that occurs when the vinegar touches the baking soda subsides.
Scrub the bottom of the toilet with a soft toilet brush. Leave the vinegar and baking soda at the bottom of the toilet for several hours or overnight.
Scrub the bottom of the toilet one final time. Turn the shut-off valve back on, and flush the toilet.