A floor drain backing up in basement areas is often the first sign, because the drain sits at the lowest point of the house and anything coming back up the pipe shows itself there. What the drain does, and when, tells you a great deal.
Madison, Wisconsin's engineering department notes that a backup usually pools around a floor drain, toilet or shower on the lowest level of the home, a basement for instance. DC Water adds that homes at lower elevations without backflow protection are most at risk when a combined sewer fills during a storm.
If the drain only acts up when the washer empties, a closer look at that single trigger covers what utilities advise.
Pittsburgh Water asks callers whether a backup only occurs during a rain event. A drain that rises only in storms points to the public system being overwhelmed. Etna's borough website describes the same sign, saying an overloaded connecting pipe can make the basement floor drain back up.
The dispatcher also asks whether the backup shows up while water is running inside the house. If a washing machine or shower is on when the drain rises, that detail belongs in your report. The City of Naperville, Illinois, adds that when only one drain such as a sink or toilet is affected and the others are fine, it treats that as an internal problem for a plumber.
A toilet overflow has its own list of household causes, and Pittsburgh Water's drain guide says wipes of any kind can clog a sewer lateral, even those labeled flushable, and that fats, oils and grease harden inside household pipes. Its rule is to flush only the three Ps: pee, poop and toilet paper.
The same guide says that when a clog forms in the lateral, it is an expensive repair that the homeowner incurs. Use the clues above rather than assuming which pipe is at fault.
The 2021 plumbing code text published for Pennsylvania says fixtures installed lower than the manhole cover of the next manhole upstream in the public sewer must be protected by a backwater valve. Whether that applies to a given house is a question for a plumber, and Pittsburgh Water says such measures are decided case by case and can make matters worse if installed badly.
Old traps in drain lines get blamed for backups too, and the post on the Pittsburgh sewer trap looks at what the plumbing code and the utility pages actually say. For context on this site, see the overview of what we do.
