I will never know how two teenage boys can dirty a tub so fast but even with all their dirt and grime they leave behind, this cleaner requires less elbow grease than Comet. It expands as it sets so it gets into all the little crevices and the peroxide disinfects too.
I made a lot because it was so dirty, but for regular cleaning, you could probably use half the recipe and have plenty.
1/8 cup lemon juice
4 pound box baking soda
16 oz hydrogen peroxide 3%
Mix baking soda and peroxide together in large bowl, then mix in lemon juice.