Take vinegar and heat for 60 seconds in your microwave until hot but not boiling. Pour the hot vinegar into the spray bottle, and add the cup of blue Dawn dish soap. Shake gently to ensure good mixing, and then spray liberally onto the surface to be cleaned. When mixed, the two compounds create a strong smell, and so I had to turn on my fan to dissipate the smell.
My shower and tub in my master bathroom were VERY dirty. I sprayed the mixture on half of my tub and let it sit for about thirty minutes. I grabbed my sponge and turned on the water. I did not have to scrub hard like I normally do with that much dirt and soap scum. The soap scum and dirt washed away easily. The photos tell the story, and as you can see the difference is unbelievable. My tub surface on the left was so shiny and clean you could see the reflection of the light up above. My shower was disgusting, and it too cleaned up nicely.