[GBSFD19]

I have been wondering for years about the round tanks on top of Ecto in the second movie. I'm looking at the part in the second movie, after the courthouse scene when they're back and they're turning right at night, and I see this big white tank on top as well as little yellow containers and I was wondering 'is it a storage tub or what?' Also, for making my own ecto, where to find them. Any info and/or help will be appreciated.