Sewer lines are underground pipes that transport wastewater and sewage from homes and buildings to treatment facilities. They are essential for maintaining public health and sanitation by ensuring that waste is properly disposed of and does not contaminate the environment. These pipes are typically made of materials like PVC, cast iron, or clay and can vary in size depending on the volume of waste they need to carry. Regular maintenance and inspections are important to prevent blockages and leaks, which can lead to costly repairs and environmental hazards.