Why doesn’t sewage flow back into your house when the sewer is full?
Your home’s plumbing is directly connected to the public sewer, so it might seem like a full sewer should simply push wastewater backward through your pipes. But what actually happens depends on elevation, sewer pressure, available capacity, and sometimes a backwater valve.    
In this video, we break down how wastewater normally moves away from your home, what happens when a sewer becomes surcharged, and why the lowest drain in a building can become the first vulnerable point when the hydraulic level rises.
You’ll see how a backwater valve can stop reverse sewage flow, why it also prevents wastewater from leaving the house while closed, and why not every home has one.  
We also explain why a sewer can be completely full without necessarily flooding your home, why plumbing traps cannot stop a serious sewer backup, and how the height of your fixtures, sewer, and nearby manholes determines where overflowing wastewater goes.  
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