First of all, I have to say this....WHO would let their tub get that dirty?!
Second of all....I made my vinegar/Dawn cleaner with regular vinegar.
I sprayed it on my tub and left it on for an hour and 15 minutes. I scrubbed with a dish sponge with a scrubby (scrubbing with the scrubby side) for quite a while, and I never felt all thrown down on with this cleaner. Perhaps I just don't let my tub get all gross? Perhaps my love affair with my Mr. Clean Magic Eraser is far too great?
I don't think I'd do it again. I'm sticking with Mr. Clean Magic Eraser once a week and an easy job.