I renovated the bathroom in our house about 10 years ago and paid a handyman friend to help me plumb in the fixtures. We cut out an old section of cast iron piping and tied in with pvc. At the time I had zero knowledge about plumbing and assumed he knew it all. The issue I have is that sometimes I smell sewer gas coming out of the lavoratory. I’m attaching a photo of the pertinent section of plumbing underneath the house.
As can be seen from the photo, the 1.25″ lav drain pipe wye’s into the 3″ toilet drain. The drain then wye’s into the 4″ vent stack before dropping down and continuing to the sewer.
I suspect the reason I smell sewer gas sometimes is that the toilet (which is not vented) must be draining the p-trap on the lav.
One thing I don’t know is whether or not the lav is vented. You can see it goes up into the wall beside the 4 inch stack. I have been in the attic and it is not revented there, so if it is revented, it would be inside the wall (is there any way to tell?)
If I don’t want to tear out my bathroom wall to vent it, could I route it differently such that the toilet does not flow past it? Or am I going to have problems no matter what until it’s vented to the roof?
Thanks,
Jon
Replies
Yeah, if the lav drain is not vented that could definitely cause your symptoms.
You MIGHT be able to study the vent routing and determine that the lav definitely ISN'T vented, but you can't really prove it is without seeing the vent pipe rising up at the lav. My guess is that it's not vented.
You could possibly install a "Studor valve" under the sink to take the place of the missing vent. It would be a stretch code-wise, but I'm guessing code went out the window a long time ago here.
What does that 4 inch vent stack actually vent? Are there other fixtures on that vent above this or just this bathroom? If that vent is just to serve this bathroom, I think it permissable to run your lav into it which would create a wet vent. Since your lav drain is substanially less volume than the 4 inch vent stack, the waste water will flow on the bottom of the vent stack while the air will still flow on the top. Would likely stop your problem without ever really checking to see if the lav is vented right now.
From the looks of it though, the lav drain and the vent stack run right next to each other, I can't imagine why someone would not have connected to two considering their proximity.
It also appears that you might be able to run the lav drain over to the capped off stub where the stool and vent drop down into the main drain. (IF YOU CAN GET THE PITCH) That should provide the air gap needed between the stool and the lav.
Are you sure its just not coming from the joint with the cast iron or from that capped off stub? I found a couple of stubs like that that weren't fully glued and occasionally I would get the same smell.
BTW, if you disconnect the lav drain under the sink and can get close enough to drain as it comes out of the wall, you can run a small drain snake UP the lav drain and find out if the pipe actually goes up or not. You might just be able to tell by getting your fingers back there and see if you just have an elbow heading down instead of a Y fitting. All depends on what was glued up and how close the stub coming out of the wall is to the actual pipe in the wall. My stubs are all terminated with male thread caps that are directly against the Y in the wall (pipe stub between fittings was just long enough to fit into both and no longer) so all I would have to do is disconnect the trap and reach back with my finger (or just look with a flashlight) to see if its an elbow or a Y.
If you stub does come out several inches, you could cut it back closer to the wall as long as you leave yourself an 3/4 to and inch of pipe to glue back another fitting.
Thanks for the input, I'll look at it some more. I wish I took a photo of the pipe inside the bathroom wall when I did the renovation 10 years ago to see if they revented inside the wall, but I would think it would have been easier to revent in the attic, so I doubt they did.
I don't know why it didn't occur to us to tie it into the vent stack (it would not have occurred to me, I was counting on the other guy to know what to do).
Thanks again