If I pour concrete over an open sewer line will this keep sewer gases in

Yes, it is old method of plugging sewer line: insert old newspaper about 8" deep and pour concrete over it. However, you can also buy dedicated cap or plug.

Yes, it is old method of plugging sewer line: insert old newspaper about 8" deep and pour concrete over it. However, you can also buy dedicated cap or plug.

Opening is to close to main line to put newspaper in if I cover it with something to keep wet concrete out of drain line, and cover all around and on top with concrete will this still work to keep sewer gas in?

OK! It's time to let us know exactly what is is you wish to plug. Open line, bald end? Hub? What? Back to you, Tom

If you don't know what you have post a pic using "go advanced/manage attachments"

You need to buy cap / plug for it. Take a picture of the open pipe, go to your local Home Depot or Lowe's and ask the "expert" in plumbing department for cap or plug. Show him the picture. He will sell you exactly what you need. This way, your sewer will be plugged /capped correctly with no chance of future sewer spill.

Let us know how it went... Milo

The opening I am trying to cap is the top of a cast iron 90. It was under basement floor. My problem is it isn't a regular hub, it has a flat surface with two notches on top, almost looks like an old style toilet flange so a cap will not work. And unfortunately there is another cast iron pipe that taps in the back side of the fitting and ends up about an 1/8th inch from the top lip so a plug will not fit inside. I have spoken with numerous plumbers, checked with plumbing supply houses, and spent a lot of time online searching for a cap that would work with no luck. Thought about breaking up more floor and replacing that section of the line, but it is tucked under basement stairs, so to do that would mean removing a portion of the stairs, rather not do that so using concrete is getting to be my only option, didn't know if that would work or not though

Now we REALLY need a picture.
It sounds like a old cast iron closet bend with a heel inlet. But I'm just guessing. Take a few pictures and let us see exactly what you have, Regards, Tom