Cleaning the plumbing with a plunger is indeed possible, but putting too much effort and not knowing the right way to use it can lead to more problems, but not a solution to the situation. Any plumbing is quite serious equipment, so I do not advise you to clean and repair it yourself, there is a good company in the Greater Toronto Area with many professional plumbers https://drainexpress.ca/main-sewer-line-replacement-service-in-toronto-gta/ , I advise you to contact them!