You will not confuse a clogged sewer with anything - it has very obvious symptoms. The most important thing is that the water does not pass well through the pipes and stagnates at the top. For example, you wash your hands and see that dirty soap suds do not go down the drain. This means that it is clogged. You can clean it yourself or use the services of professionals https://pomplumbing.ca/snaking-and-powerwash-for-clogged-drains/ , I personally prefer the second option.