This is what you're looking for:
http://www.teachersource.com/product/preforms-and-caps/chemistry
It's the same thing as a White Labs vial. They are the beginnings of a 2l soda bottle (which then gets melted and expanded). PERFECT and cheap for yeast.
I do something similar. I bake a couple cans of pumpkin, throw it into a nylon bag, and leave the bag in my kettle as I heat my strike water. If you leave it in there long enough, and move it around, the water definitely turns orange and takes on the pumpkin texture. Sure beats those...