1. Pour Coke into the bowl. Pour it around the rim so it flows over the stains around the inside of the bowl.
2. Let it sit for at least an hour. The acids in the Coke will break down the stains. For extra cleaning power, let the Coke sit in the toilet overnight.
3. Optionally, clean the toilet with a brush. If there are lots of stubborn stains, you may need to use a brush to further loosen them before going to the next step.
4. Flush. At least some of the limescale buildup should be dissolved by the phosphoric acid in the Coke.
Try conventional natural toilet cleaners if problem persists. While Coke can remove some sludge and buildup caught in your toilet bowl, it's not the most effective cleaning agent. The sugar in the Coke can also leave the toilet bowl sticky and be a vector for other bacteria. Here are some other natural cleaning solutions that you can try.
- Try mixing 1/2 cup vinegar and 1/4 cup baking soda (or 2 teaspoons borax) into 1/2 gallon (2 liters) jug of water. Store and apply to toilet bowl, scrubbing and waiting an hour before flushing.
- To attack mold, try mixing one part hydrogen peroxide with two parts water in a spray bottle. Spray onto moldy surface, let wait at least one hour, and scrub until mold dissolves.
- Try a mixture of two parts borax and one part lemon juice for another versatile cleaning agent. Apply to toilet bowl, let rest an hour, and scrub off deposits.
- Since Coke has sugar (or high fructose corn syrup) in it, be sure to rinse the toilet afterwards. Bacteria love sweet stuff, and might be all over the Coke residue.
- If you have roommates or a spouse, be sure to inform them about what you are doing. Otherwise, they may think you had some sort of "black thunder" diarrhea and failed to flush, and will flush it for you, thwarting your altruistic cleaning efforts.