I live in a house from the 60s that somehow never had a back flow valve. My insurance company is pushing me to get a back flow valve installed before they will provide basement flooding insurance.

The house has a single water inlet pipe and a single sewer outflow pipe.

I just had a plumber come to give me a quote for installation and he said that i'd need a back flow valve at each location where I have appliances or drains installed in the basement.

This sounds bogus to me; back flow valves are to prevent sewer water entering through the drain; right? There's only one drain, so only one valve is needed; correct?

Is he taking me for a ride?

1 Answer 1


A single backflow valve placed in your outflow line would be all that is needed to prevent sewage from the city main backing up into your house. It sounds like this is all that would be necessary to satisfy the insurance company, but you'd have to ask them.

Multiple backflow valves would be designed to prevent a blockage in one of your internal drains from causing a drain overflow in the basement. Ask the insurance company if this is what they require.


Back-flow valves are not required in my neighborhood of slab-on-grade houses in Dallas, but I have installed a spring loaded overflow in my cleanout in the yard. This protects me from a backup in the sewer under the street in front of our house, but this simple device ($4.00) of course wouldn't work to protect a basement.

The streets run east-west and the terrain slopes down from east to west. The neighborhood is bounded on the west by a street running along a park around a south flowing creek. Two houses on two different streets north of us have filled with sewage inches deep due to a blockage in the city lateral where it enters the city main under the creek bottom. This was decades apart in time. The sewage from uphill filled up the main under the street and then out the shower and toilets of the lower of the two houses at the west corners.

I knew the people in both houses and it was a horrible mess.

  • Thanks for the reply; I had not considered that the cause of the flood might be local.
    – JanSolo
    Sep 28, 2017 at 21:00
  • It's bound to be much more expensive to put back-flow prevent valves on all the drains in the basement in addition to one in the main drain to the city sewer. You should ask the ins company what they require and if they only require only the one on the main drain, then ask around about whether putting them on all the drains in the basement is more trouble than it's worth. What drains do you have in the basement? If you have a toilet, then I would think the cost would be high to put a backflow prevent valve in that line. Sep 28, 2017 at 22:00
  • 1
    I have never seen more than 1 backflow on the sewer if it is local (from your use you can turn the water off and no more back flow) make sure the back flow device is accessible after install (they do need maintenance / cleaning at times).
    – Ed Beal
    Sep 28, 2017 at 22:54

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