According to Twitter user @OddPittsburgh, this "Pittsburgh Potty" photo dates back to 1922.

Old homes are often full of outdated features that seem bizarre in a modern context but served an important purpose at the time of construction. With some of these quirks – such as milk doors, dumbwaiters and boot scrapers – the utility is obvious. With others… well, not so much.

One such eccentricity from a bygone era is a case of curious plumbing. In some old homes, usually only those dating back to before the Second World War, a random toilet can be found in the unfinished basement. This toilet generally has no walls around it and is sometimes accompanies by a rudimentary shower or sink, but often neither – talk about a serious lack of privacy! If that weren’t odd enough, the placement of the toilet is often strange, such as wedged against a foundation wall where it would be extremely uncomfortable to use.

These toilets are particularly common in pre-war homes from the Pittsburgh, Pa., area, which is how they came to be called “Pittsburgh potties.” Local folklore frequently links the potties to the city’s history as a steel town and ascribes them a mudroom-like role. The belief is steel workers would come home at the end of the day and head straight to the unfinished basement – through a separate entrance, so they didn’t track dirt through the home – to clean themselves up and change out of their work clothes before joining the family upstairs.

However, this doesn’t quite explain why this design quirk extends to homes in cities far from Pittsburgh. It turns out the toilets served a more important role and likely weren’t meant to be used at all. When these homes were built, city sewer systems were crude, unreliable and prone to backups. When backups occurred, sewage would enter homes and overflow from the fixtures lowest to the ground, so the basement toilet acted as a safety valve – placed right above the sewer line where it came in from the street. This way, the Pittsburgh potties prevented any nasty messes in the finished areas of the home by containing sewage backup to the unfinished basement, where the concrete floors were much easier to clean than a nice bathroom or kitchen.

Thankfully, plumbing has come a long way since then. As a result, many old basements that once housed a Pittsburgh potty have been remodeled and refinished, with the seemingly useless toilet removed or replaced with a more practical fixture. However, some Pittsburgh potties live on – destined to confound homeowners for years to come.