The story
* New Orleans architectural historian Samuel Wilson, Jr. has suggested that the term alludes to the idea that if all the doors are opened, a shotgun blast fired into the house from the front doorway will fly cleanly to the other end and out at the back. * Folklorist John Michael Vlach has suggested a corruption of a Dahomey Fon area term "to-gun", meaning "place of assembly", brought to New Orleans by Afro-Haitian slaves.
Etymology from Wiktionary, CC BY-SA 4.0.