Originally Posted by slownsteady
If you think about it, that whole assembly is a little wonky. It looks like the main drain goes off at floor level to the left, so why are all all those pipes above going to the right? Looks to be about 8 feet too much pipe in that run.
It used to go from the toilet upstairs to the left and then down to the dran at the floor and someone just cut and changed the direction to allow for the sink in the basement, out of sight to the right.
And then we don't see a vent pipe coming back from that sink so that could be the problem with sewer gas.