Found via Google in reply to a request. Rinse agent is the blue liquid you add to your dishwasher once a month. Jet-dry is the most popular brand but Cascade also makes one.
Ingredients:
1 cup vinegar
1/2 teaspoon liquid dish soap
1/4 cup rinse agent, jet dry
Directions:
1. Mix all ingredients together. 2. Pour into a spray bottle. 3. Use daily to keep shower clean.