Drain through floor/trap/vent gas smell.... question?

[KnowsNothinng]

Morning all. I have a house built in the late 40s. I think at some point the plumbing was semi updated. But much of the lines are cast so I don’t know when. We have a kitchen sink that has its own drain and vent. However the drain, instead of going through the back then to the basement it goes down through the floor. So I basically have an s trap going on. The vent doesn’t connect until down in the basement either. So it goes down to the basement then over about 3’ to a T where the drain line goes down and the vent line goes over another 3’ to a cast vent all the way to the roof. We randomly get a gas smell which seems to be worse in the mornings. Is this setup causing the water in the trap to be siphoned?

 

[hj]

Yes, that "vent" is completely useless and has no function. You cannot just connect a vertical pipe to a drain line and call it a "vent".

 

[Sponsor]

 

[Reach4]

If you post a photo of the area under the sink. somebody might propose a layout where you add an AAV (air admittance valve) to do the vent function.

 

[KnowsNothinng]

Yes, that "vent" is completely useless and has no function.

Pretty much what I figured. Seems like the inspector could have pointed that out when we bought the place. So short of a complete redo am I stuck? We can’t even have the vent closer due to the window above the sink.

 

[KnowsNothinng]

Let me know if any better shots are needed and I’ll try.

 

[Terry]

Yes, what you have will siphon.
You can add an AAV under the sink to vent the trap. It should be at least 4" above the trap arm for the trap.

This one was for a bathroom lav.

 

[Reach4]

You also have the alternative of drilling a new hole through the cabinet and floor to put the drain line wherever you want.... But the hole you have should serve. The disposal can be rotated to put its output in a better spot for your new solution.

 

[KnowsNothinng]

Thank you for the response! I’ll set it up with an aav. Pretty sure when the previous owner had the kitchen remodeled they had a plumber come in and do the work. I vaguely remember seeing a recipet in the stack of stuff she left regarding the redo. Makes me wonder if they are still doing work.