BusyBodyHealth

Bathtub and Shower Cleaning Gel (not on shower doors)

1 cup white vinegar; hot
1 cup blue Dawn dish detergent

Place both in a squirt bottle (I used an empty shampoo bottle), and shake to create

a gel. Squirt the solution all over your tub, and allow to sit for a few minutes. You can even let it sit overnight if you have some really hard to clean spots. Wipe off with a sponge or rag, then rinse.

Source:
http://newlifeonahomestead.com/2012/07/homemade-showertub-cleaner-gel-recipe/