Drain lines and sewer lines are both parts of your home's plumbing system, but they serve different purposes.
A drain line is a pipe that carries wastewater from your home's sinks, showers, tubs, and other fixtures to a central point, such as a septic tank or sewer line. Drain lines are typically smaller in diameter than sewer lines and are designed to handle only wastewater and small solids.
A sewer line, on the other hand, is a larger pipe that carries wastewater and solid waste from your home's drain lines to a treatment facility or municipal sewer system. Sewer lines are designed to handle larger volumes of waste and are typically made of more durable materials, such as PVC, cast iron, or clay.
Another key difference between drain lines and sewer lines is their location. Drain lines are located within your home's walls and under your floors, while sewer lines are buried underground and typically run from your home to the street.
Drain lines and sewer lines both serve important roles in your home's plumbing system; they differ in terms of their function, size, materials, and location.