What is the whiskey still illustration about Adam and sin?
The whiskey still illustrates the old Adamic nature as a producer: the still itself does not bend minds, but what it produces does. Likewise Adam is the source, and sins plural are the results of that nature. Sin singular describes the Adamic nature; plural sins are its output.
Les teaches that the old whiskey still is one thing, but what it produces is what bends people's minds. The still is out there; it is the producer. Yet the still itself does not cause people to get drunk or have their minds bent; it is what the still produces. He says it is the same way with old Adam: Adam is just like that old still, and it produces sins, plural. In the context, sin singular deals with the old Adamic nature, while plural sins are the results of that Adamic nature. So the illustration distinguishes the Adamic source from the sinful activities it produces. He then says that when we were dead in the activity prompted by old Adam, He has quickened us and made us alive together with Christ by grace, not by works.