How to Plug Your Sewer Line

You may need to plug your sewer line during a disaster as a back flowing sewer can cause considerable property damage and pose health hazards.

In floods and other disasters that affect the sewage pumping stations you may save your basement or house from backed up sewage by plugging your sewer line. However, stopping the sewer is rather tricky since there isn't simply a valve you can turn off.

The down side to doing this is, well, your sewage does not flow OUT of the house either! You will want to shut off the water supply to prevent anybody from flushing or running the tap while the sewer is plugged.

Purchase a Sewer Test Plug

You will need to prepare for this procedure ahead of time. Purchase an inflatable sewer line "test plug" that matches the size of your main sewer pipe (commonly 4 inches, at least in most of the USA). You can check the local hardware store, but you will probably need to go to a plumbing supply store or find one online. Make sure you have a hand operated pump designed to inflate the plug.

Inflatable sewer test plug

I did find an online source for plumber’s test plugs if you can’t find one locally.  Look for the single diameter models without bypass ports for your size of pipe (they are cheaper than the multi-sized or bypass models).  These use a standard bicycle tire pump to inflate.

Find Main Cleanout

To plug the sewer you need to find the main cleanout going out of your house.  Make sure there are no drains after the cleanout or you will need to plug those too.  (I have a floor drain in my basement that is after my main cleanout, so, I need a 4-in plug for my main drain plus a 1.5-in plug for my floor drain.)

Main sewer cleanout in a house with a basement
The top of the test plug should be below the blue line

Plugging Procedure

• Notify the entire house that you will be plugging the drain and explain the ramifications of such as procedure.
  
  
• Verify that the water supply is off so you don’t run water down the soon to be plugged drain.
  
  
• Remove the cleanout cap using large wrench or pair of pliers.
  
  
• Tie a rope to the sewer plug bracket so you can later retrieve the plug from the pipe.
  
  
• Insert the plug past the connecting pipes toward the direction the liquid normally flows.
  
  
• Inflate the plug with a bicycle tire pump.
  
  
• Repeat for any other drains after the main cleanout.

That should stop the flow. But, as I mentioned, it stops it both ways. You will need to come up with an alternative to using the toilet to go to the bathroom. Tape the lid shut on the toilet in case somebody forgets that it doesn’t work anymore.

Septic Systems

Although somewhat rare, septic systems can also backflow if the septic drain field floods and certain other conditions are right.  More common than backflow would simply be the septic system backing up, as new waste has nowhere to go because the drain field is flooded.

The solution here would simple be to quit flushing and running water down the drain until the drain field is no longer saturated.  (Try turning your water off to help accomplish this.)

If your septic was back flowing you could use the same plugging procedure as above.