Sewer backup into house - Vent Problem?

[PJ Brady]

Hello! I have a 2 family home in NYC. Going on 14 years of home ownership. After hurricane sandy filled 5 feet of water in our finished basement, we installed a backflow preventer on the sewer main inside the house. In the last couple of years we have had a gurgling sound coming from the rain vent outside our basement steps. The rain vent is directly connected to the main line under the foundation. I assume the gurgle is the sewer line pulling in air to properly move the sewage.

We brought in a plumber to clean out the lines twice in the last 4 years, and it seemed to work and stop the gurgle. Recently the gurgle has returned. Our usual plumber was not around, so I called in a new guy. He looked at the backflow preventer and said it was installed wrong and was creating an air venting problem. He opened the cap on the street cleanout (top of the photo) and immediately you could hear an air hissing sound. He snaked the line to the street, charged me 150 bucks and left.

The gurgle came back the next day, and was so bad our basement toilet was gurgling and black water came into the bowl. Water also backed up from the rain vent outside and came into the house. The reason for all the water was that my wife and mother in law were both doing laundry. There are clothes washers in the basement and one on the 2nd floor (in laws). This is the first time water has backed up in a year and a half of having 2 washing machines.

Any ideas on what the venting problem could be? Is my backflow preventer installed wrong? Appreciate any help.

PJB

 

[Reach4]

Any ideas on what the venting problem could be? Is my backflow preventer installed wrong?

Flapper type check valves, which I think is what you have, will often not seal well in the face of a backup. Stuff gets in the way, preventing the flap from fully sealing. I am not saying this is related to your gurgling.

If you Google search for the term "normally open" backwater valve , you will find discussions on that. I am sorry to tell you this. I am not a plumber. At least don't cancel your sewer backup insurance.

It might help to clean the flapper seat before flooding is expected. While you have the screws out, I would measure and buy some new screws in case the heads of the ones you have get buggered. hex head or cap screws (Allen head) might good choices, since they are less likely to be damaged than Phillips head.

 

[Sponsor]

 

[WorthFlorida]

If it was installed wrong, from day one you would have problems. There is some kind of backup past the backflow to the street connection or the street side of the sewer is backing up into your main. The flap that stops the water from backing up is closed and pressure from the street sewer water is coming down the pipe to your house. Any air is trapped inside the pipe and since the flapper is closed, therefore, air in the pipe is what you are hearing escaping.

Snaking the line is probably not good enough. It can goes past blockage and leave only a small hole through the plug. Possibly the pipe has a dip in it causing water to keep the pipe partially filled with waste water. This can cause solids to remain in the pipe. Another possibility is the street sewer is backing into your main. May be time to have the line checked with a camera.

It does seem that backflow is working in your favor. You might want to call the city to check out the street on this, but right now that probably isn't possible. I'm surprised that the city didn't require to have the rain gutter disconnected from the sewer connection.