Take a spray bottle and fill it halfway with white vinegar. Heat in the microwave. Fill the rest of the way with blue Dawn. Put lid on and shake to mix well. Spray on your tub and shower walls. Allow to sit for a few minutes and rinse away. It will totally melt all the gunk, slime, sludge and other stuff that builds up including a bathtub ring.
Click here for an awesome article . . . Original Blue Dawn, Not Just for Dishes Anymore from the blog One Good Thing by Jillie, where you will find a listing of lots more uses for Dawn that will save you money!