Oh Good Seasons, oh how I love you. I have yet to find a bottle of pre-made salad dressing without milk or soy. Soy lecithin keeps the ingredients from separating. Useful for them. Pain in the booty for me.
The first time you use it you buy the kit with the marked bottle included. The marks tell how much water, vinegar, and oil to add. After that all you have to buy is the refills.
Change the type of vinegar you use and you get a different flavor.