To read a home sewer system diagram, find the cold water supply lines by identifying the lines that feed from the municipality water main to your home. Find the hot water lines by first locating the hot water heater and following the lines that flow from it to faucets and appliances. Find the drainage system, identify the lines that slant downward for waste removal. The diagram also labels the traps or seals of the system.
The cold water lines are the ones that go through the water meter. The meter tracks the water usage for the whole house. After it passes the meter, the line branches throughout the home to plumbing fixtures and appliances. The hot water branch lines are usually parallel to the cold water branch lines as they both run to the same places.
The drainage system moves the waste water and sewage from the home to the sewer drain. A home diagram marks these pipes, vertical stacks and horizontal drains specifically, indicating that water flows away from the home. A diagram also marks the traps as U-shaped pipes under each fixture, and the connected vents. These prevent sewer gas from leaking into the home by trapping water in the bend.