When you have a major blockage in your sewage line, it is an emergency. Sewage backing up in your home can do serious damage to the building, and it can cause serious ill health-effects for you and your family. So naturally, you would want to have the problem fixed as soon as possible, and in most cases, this will probably require the help of a plumber.
One way in which they might fix the problem is by accessing the sewage line through the sewer cleanout. Usually, you will find this access point near where the sewage leaves your home. The first place to look for the sewer cleanout would be near your downstairs bathroom. In colder weather, it might be located indoors, but if you live in a warm climate, then you will probably find it outside the house.
The pipe usually is sealed with a lid that screws on with a square peg on top of it. This is so it can be opened up with a tool specifically made for it.