herebedragons writes:
If you have a clean-out fitting between the kitchen sink and where you know the drains to be clear, try running the snake from there.
I have a clean-out plug in the basement, directly below the kitchen sink. From there, the drain seems to wander around under the basement floor until it finds the main drain. (It probably vetures under your house too at some point.) Snaking from there sometimes reaches clogs.
Like some others here, I'm skeptical about mild chemicals attacking ferocious clogs. The "explanation" that I would offer is that IF it works it's because of a combination of three factors: reaction of acid with whatever acid reacts with, reaction of bicarbonate with whatever bicarbonate reacts with, and mechanical action provided by carbon-dioxide pressure.