Unlike your feed lines your waste lines are not under pressure.
This means that you must always maintain a downward slope when installing waste lines. Never run a waste pipe within a floor or wall at the horizontal this will be asking for future trouble.
When you install Waste lines in your house you can use PVC or Cast Iron pipe. Today most builders prefer PVC because it is light easy to handle and goes in quick. Cast Iron is still used for noise reduction or where required by code.
When you install vertical waste line you should support the lines with metal strap by attaching to a fixed wood member not less then every 4 feet.
When you are going through a floor structure you should use a fire stop to prevent the travel of flames from one floor to another.
To the right you can see a double waste line being installed in a ocean front home in New Jersey. One line is for sewage the other is for rainwater that is collected off the roof of the house. If rain water was not collected and pumped out to the bay then the streets would have a larger flooding problem.
You should never mix rain water or sump pump water with your sewer line. In time of heavy rain you will overload the system and you may endup with a street full of raw sewage.
Waste lines inside the house that are mounted horizontally should have at least a 1 inch in 8 foot slope.
If you are installing a waste line in a floor the horizontal run should be the shortest distance as possible to a vertical pipe so that you can maintain the slope of the pipe.
If a fixture or appliance is below the main waste line you will need to use a brown water or sewage pump to raise the water to a level higher then your waste line.
Clean out pipe access should be provided at any point where you have a sharp bend. Cleanouts have a screw cover and allow you to gain access for mechanical cleaning.
You should also install a cleanout at the point where the main waste line exits the house.
Venting Waste Lines
When you were a kid you probably took a straw full of soda and with your finger over one end you could pull it out of your glass and the soda wouldn’t run out.
This is the same problem found in Waste Lines. Although the water has downward slope the air displaced by the water needs to escape.
If you look on any building or home you will see pipes sticking out of the roof. This is the venting for the waste lines.
Each branch will need its own vent this means one for the kitchen and each bathroom at minimum. If your architect plans correctly they will place all of your plumbing in a central location. This will reduce the need for many waste and vent lines because they can share them in the same wall.
In other howtos we will cover how to make connections for different appliances and fixtures.
Designing a plumbing system is much harder then installing or repairing one. Although it is not rocket science all new homes require a separate plumbing plan be submitted and it must be in 3d to allow the inspector to understand if proper flow rates and slopes have been designed.
For this reason it is best to stick to the Architects Plan and install to their recommendation.