This works fast and easy; I just made up a batch and it cleaned my tub with no elbow grease required at all. I found the recipe here.
1 2/3 cup baking soda
1/2 cup castile soap — I used lavender Dr. Bronner’s
1/2 cup water — I made mine hot
2 Tbsp white vinegar
Pour the mixture into a clean bottle — or pour the ingredients into a clean bottle, like I did, and then stir with a bamboo chopstick and shake it up. Shake well, squeeze out onto your bathtub or sink, scrub with a sponge and rinse with water.
Voila! Clean and natural tub.
I put mine in a spray bottle with a dysfunctional sprayer top. Nevermind the sprayer; it doesn’t work, and this recipe is thick and creamy and would never spray. I may hunt around in my recycling bin to find a screw-on lid that fits the opening.