Before calling a technician this time, only to learn the culprit was a hairball in a sink drain, I decided to troubleshoot the plumbing problem myself. I consulted resources and learned that my home's drain, waste, and vent system took advantage of gravity and was designed so that water into my home's drains flowed downhill from start to finish. The waste water from each sink, toilet, shower, tub, and appliance collected into ever larger pipes, finally merging into the main sewer line from my home to the city sewer. Based on my research, the fact that I had two sinks$,$ a tub, and the toilets all backing up indicated that the solution was beyond a few simple doses of chemical drain cleaner this time. Instead, it was more likely that there was a clog in the main sewer drain from my home, meaning tree roots, a damaged pipe, or a major clog was responsible.

According to the passage, which of the following is true about the author's plumbing problems?