A major block may be caused by large items failing into the drains, or tree roots breaking into the drain system. For any of the major types of clogs in the main system a heavy duty sewer snake should be used. The two types of large snakes are a hand operated or electrical powered snake. These items can be rented or purchased. This often is a job for a plumber. You do not want to damage the line running out of the house.
There are three ways to access a major clog:
Lifting the toilet which is a procedure that will access most of the system.
In most newer homes there is an outside clean-out plug to access most of the system. Just locate the cap, unscrew the cover and put the power snake through the system.
Through the main roof vent for the entire system. This is the hardest to access and power tools can be a problem depending on the roof incline.