10 years ago, when I still frequented Baltimore and dated a woman in Fells
Point, I noticed that it was normal for the rowhouses there (she owned one)
to have an 'outhouse' in the miniscule back terrace which, either
originally or as a later conversion, contained a flush toilet. As these
terraces usually were surrounded by high walls, privacy was assured on the
way to & from. Evidently this was usually the original way that a toilet
was provided in many working-class houses. Some of them were still in place
and in working order, used as a backup to the later in-house installation;
others had been removed and the outhouse (usually or brick or cinderblock)
converted to a storage shed or removed. 

Edgar Allan Poo