Sewer lines can back up for many different reasons, including clogs from foreign objects, poor airflow, intrusion of tree roots, broken pipes or simply improper design. Just like any drain line in your home, a sewer line can get a clog. When it does, the end result is that your drainage system backs up. Clogs can occur when there is a buildup of foreign substances, such as hair, food, grease, or beauty products, getting into the drainage system. Of course, small toys sometimes find their way into a toilet, creating a messy situation that often requires a plumber's help. In addition to foreign objects getting into your system from inside of your house, nature can find its way into your drain lines from the outside as well. Over time, dirt and debris can enter the pipes through small cracks that inevitably appear through wear-and-tear or old age. Tree roots, continuously applying pressure, can break through a pipe's exterior, or find small cracks and infiltrate your sewer line in pursuit of water. Upon finding an excellent source of water the tree roots will continue to grow,taking up more and more space inside of the pipe, simultanously bringing in dirt and small stones with them. Eventually, the blockage becomes impassable, and your sewage backs up onto your property or inside of your home.An improper design for your drain system, such as poor sloping conditions, can prevent gravity from doing its job of channeling your waste water into the sewer. Another design flaw could be a lack of proper air flow built into the system which can create a backward suction that prevents your waste water from draining properly. Right angles or hard turns in your drain system can also restrict the flow of waster water and lead to the accumulation of matter, which will also lead to clogging or slow running drains. Of course, there's always the unusual circumstance of the city sewer being completely backed up and preventing your sewage from entering it. Aging pipes that have outlived their usefulness can also cause your system to fail. Old pipes that become thin and brittle can crack or break, leading to inefficient drainage or stoppages.The best way to figure out which problem your sewer system is experiencing is to bring in a professional plumber to diagnose the issue. Plumbers can use specialized cameras to explore the drain lines in search of cracks, breaks, or obstructions in your pipes. Once identified, the proper tools and processes can be used to get your drains flowing again, as they were intended to.