After your second visit to Mean Street South, on the North side of the area you will find Gremlin Jamface by a weird contraption by the Penny Arcade. He asks you to give him some scrap metal so he can repair the device. It may take you a while since you need to collect over 100 scrap metal. Once repaired it leads to an entrance to the underground
Nearby there is a machine for fireworks. Bring them over to the broken elevator and ignite them. They will explode and destroy the elevator sending scrap metal all the way over to the broken Fishead Hut.