There was a recent thread that answered this question. The answer was that the entire song consisted of two verses. The first verse was the line "This is the song they sing at the sing-song ins Sing Sing" sung over and over to the tune of She'll Be Coming 'Round The Mountain When She Comes. The second verse was the line "This is the sing they song at the song-sing at Song Song" sung over and over to the same tune.
Don't blame me. I'm just reporting what someone else posted. You can look it up.
Jacob