I just moved into a house we recently purchased. In the remodeled basement is the laundry area. The original washing machine drain, which is in concrete block wall, has been eliminated and another drainage system installed on the outside of wall with its own vent. It isn’t tied into the septic. The original one is. A couple of says after moving in, we started getting the smell of septic gas. I narrowed it down to the laundry area. I located the original drain line and thought it was probably covered over and not sealed. I was right. They had cover the whole area around the top of the pipe with insulating foam. I removed the foam and there was no seal on the pipe. I used an expansion plug and sealed it. It seemed to stop the odor in that area. Next day, I had been away from the house for a while and when I walked in I could smell the odor in the house. I’m thinking there is a problem below the top of the pipe which caused the previous owners to stop using it. They said they had the system smoke tested and didn’t find a problem. Now, my question. Would it harm anything to force a ball I’d foul down the pipe to about floor level and fill the pipe with concrete? I think the crack or break in the pipe is allowing gases to deep into the walls way below where I could cap it.