I Don't KNOW what it means. John Cohen of the NLCR has speculated that it takes a lot of wood to keep a still running and that the original word was HAUL the woodpile down and that it's really a song about making moonshine. I hear the words somewhat differently from Stewie, and like his interpretations better than some of mine! The Holy Modal Rounders (who, thanks to a posting on Mudcat, I am going to get to see for the first time in some 30 years on Saturday) add some extra verses, one of which goes, more or less, Amanda, you're a crazy witch (Hold the woodpile down)
You make me want to jump and itch (H t W D)
You turn my brain into a fog (H t W D)
Oh, let me be your salty dog (H t W D)

I don't think it NEEDS to make sense.