The One-Minute Decision Is the problem water coming IN or waste not going OUT? Water coming in where it should not = emergency plumber. Something on the supply side has failed. Water is spraying from a pipe, dripping from a ceiling, pooling under a water heater, or running from a fixture that will not shut off. The water is clean not sewage. The problem is pressure, a break, or a failed valve.
Start with the normal pattern: wastewater should move away from the fixture, through the branch line, into the larger building drain or sewer lateral, and out toward the public or private collection system. Most confusion starts when one symptom is judged without locating where that pattern is breaking down.
For emergency drain cleaning questions, the useful first step is separating a local fixture issue from a deeper line condition, because those two situations can look similar at the surface but lead to different next steps.