Our laundry room sink has this bizarre attachment to to the back of the drain line clean out. It would almost seem like it was or is supposed to be a vent. Recently it’s started to give off a foul sewer smell when our washing machine rinses.
Can I safely plug it? Maybe remove it if I can manage to pry it off? When I asked our plumber what it was, he just smirked and said it was a “crazy thing.”
It’s strange that it has a 90 for the clean out and also has an open connection on the right. If this is a vent stack it should be stinking up the place always. I guess maybe when the washing machine drains it creates some negative pressure that causes methane to leak in. If the vertical pipe is actually a vent stack you should be able to plug the open connection on the right side. Another comment is make sure any p trap has a bit of water in it. Traps will also leak methane when they start to dry out.