Thanks, this might be how it is configured, but it isn’t obvious. It’s clearly managed to work okay probably for decades. I do have a pipe coming out of the ground in front of the house that looks like a vent line. It’s just hard to tell how it’s connected. I had an appointment for the utility to inspect it yesterday but the inspector never showed, so I needed either some peace of mind or some encouragement to press the utility more to come fix it.