Anything that should not be in a sewer line has the potential of causing a blockage. For example:
Kitchen grease, disposable diapers, and sanitary napkins can accumulate and cause a blockage.
Tree roots seeking moisture can grow through cracks in the lines, causing a blockage.
Vandals have stopped up lines by putting bricks, wood, oil filters, bed springs, and even Christmas trees in manholes.
Illegal hookups allow excess water into the lines. Outside stairwell drains, sump pumps, roof leaders, and drain gutters should never be connected to the sewer system. A sewer system is designed to carry a predetermined amount of sewage. Rainwater not only overloads the system, but also raises the cost of the treatment process.