Plumbing Drainage System
Getting the Waste water out
The drainage system, in my eyes is the most important part of the plumbing system. Some may ask why I would value it more than the fresh water system? My reasoning is that I would always prefer to carry clean water in, over dirty water out. Either system can be troublesome and costly for repairs and both can cause considerable damage. If we think about what the drainage system carries out, we realize its very important that it stays in good shape and is properly maintained.
The building or home drain, stops two feet outside your home and connects to a sewer line which connects to a street sewer or a septic system. The important part here is that when I say building drain its understood this is the main horizontal sewer pipe extending through the foundation and it ends at 24 inches from the buildings foundation. The drainage systems other termination and transition points will be explained or understood as I explain and describe each systems purpose.
Your plumbing needs air flow
The vent system connects to the drainage system in many places and the drainage system would never work without the vent system so we will also provide some information on it here. But you can find out more by reading our article "Plumbing Vent System"
So now lets get on with the good stuff. Lets start by talking about how the vent system and drainage system work together to remove dirty water from your home. As I had said, these systems work together. The vent system is connected to the drainage system at vital connection points that allow the vent system to do its job (To let air in and out) and the drainage system to do its job. (Get waste water out)
The vent system breathes for the drainage system, if the drainage system does not get enough air it will drain slowly or not at all. See or try the example I have shown below. Its easy to do, you can get a straw or any tube and test it yourself.
For this exercise you will need a tube or straw and a container of water. Just immerse the tube in water then raise the tube from the water while holding a finger over one end. You will notice very little or no water drains from the tube. Now release your finger from the end of the tube and all the water will evacuate.
Below is a movie showing how it works.
If you can imagine your drainage and vent system working as the straw in the glass of water did. You can imagine the issues a plumbing system could have if not properly vented. A toilet with a vent plugged or improperly installed will flush very sluggishly and will often clog with few solids introduced.
This is only one of many potential issues and you can read more on the venting system page and through the plumbing consultation website.
In rare cases birds or other animals can plug up roof vents. If these vents are plugged then air can not get into the systems it serves, and the drains will not function properly. The same thing could happen if a vent is missing or undersized.
Ok enough about vents, lets talk drains.
Below I have included a basic diagram of a drain and vent system in a home. The drain system is represented with a black line and the vents are represented with a light blue line indicating airflow.
Plumbing Waste and Vent Diagram
Installing drainage fittings
When installing or upgrading a drainage system you should first size the system by evaluating several factors. Factors include the type of fixture being connected, number of fixtures being connected, and distance of fixtures from the sewer pipe.
Fixtures are assigned fixture units.
Drain and vent fittings must be installed in the proper direction. Below you can find some examples.