Additional opening along with basement sewer clean-out

[splash78kas]

Hi All,

I am homeowner in NJ. Over the weekend, we got rain for 2 days straight and I had some water backing out of one of the sewer related openings. There are 2 openings in my basement floor. One seems like a clean-out. Not sure, what the other bigger opening is for. In the pic, the mysterious opening is the one which is open and looks dirty.

Any ideas, what the second hole is for and how to prevent rain water from backing up again in future from here.

Thanks !

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[CT18]

The one with the cover off I believe is a backwater valve, to prevent water from backing into the lines in the house. Under the next cover should be a swinging gate that can be serviced or replaced The one with the cross is the cleanout.

 

[Homerbplumbing]

That is a Backwater valve. It is used to prevent sewage from backing up into a basement when public sewer backs up. They are not the most reliable devices. There is a flapper inside it that closes when water flows in the opposite direction of intended flow. They are notorious for not working properly. The lid should have an o-ring on the underside of it to seal it however debris and or over tightening can cause it not to seal.

The rain water could also be seeping in through the riser pipe from under the slab. The riser pipe that goes from the the top of the fitting to the top side of the concrete slab where the lid goes onto it usually not sealed.