View Full Version : Help With Adding A Vent

07-16-2010, 01:35 PM
So I'm working on a bathroom that was finished to about 90% by the original contractor. I'm trying to finish things up but want to make sure I do things correctly.

I always assumed the vent was connected, as I said they did 90% of the work, but as I was flushing the supply lines, I dumped the bucket of water into the tub and it would not drain. I figured it may have a little bit of debris because this bathroom has been sitting unfinished for almost eighteen years, but I began to think the vent wasn't connected and sure enough it wasn't.

So I've posted a video, and I'll offer an explanation as to what you are seeing:


The first thing is the drain line for the sink. The second is the drain line for the tub which has a p-trap. The third thing is the drain for the toilet, this main part is where the tub drain connects, and it also branches out on the other end, I always assumed it was for a cleanout, but apparently it was for the vent. You can also see the unfinished connection between the toilet/tub connection, and the sink. Lastly the video goes sideways and you can see the unfinished vent. The vent does tee off and connect to the sink above the ceiling.

I just want to make sure I connect it correctly, I have a feeling it wouldn't be right to just bring it down the the concrete, elbow it and connect it to the line where the toilet is, but then again that might be the right way. If that is the right way would I put a cleanout instead of an elbow?

I figured it was wrong because the toilet or tub could back up into the vent, but at the same time those drains need air behind them to work properly.

I also did a paint mock up if that helps:


07-16-2010, 02:09 PM
Okay so I was looking around and went through the "scrap" pieces of PVC that were left behind and I was thinking this may be what they had in mind:


The first new piece is like a Y with a cleanout, the other new piece is an elbow with a reducer. Would that setup be good once all glued together with whatever pieces would be necessary to finish it off?

07-16-2010, 02:17 PM
The picture below should have been a combo or wye with 45, not the Santee that I'm seeing here. Whenever you go from vertical to horizontal, it needs to be a wye fitting.
If the tub is not draining, there may be a mechanical plug or test cap somewhere.

Each fiixture should have a vented trap, it's a little hard for me to figure out what I'm seeing here.
The lav would work for wet venting the tub or toilet if it's run in 2", and if it's laid out correctly, little hard for me to see that though.


Wally Hays
07-16-2010, 02:19 PM
They roughed it 18 years ago?

It's real hard to tell from the pictures and diagram what is going on there but if the tub isn't draining it probably still has a cap or test plug somewhere. Vents won't cause that problem. No vent piping can run horizontal until it has risen to a point 6" above the flood level rim of the fixture served.

07-16-2010, 02:30 PM
Yeah there are receipts from 1992 so that's about eighteen years ago. It's still hard to tell what's going on between the two pictures and the video? I was really trying to make sure it was obvious what was going on.

07-16-2010, 02:39 PM
Hopefully this helps. You can't see the vent in the first picture because it's not connected as I mentioned. Also as I mentioned the vent on the sink connects in the attic space to the vent you cannot see.




07-16-2010, 03:07 PM
The picture below should have been a combo or wye with 45, not the Santee that I'm seeing here. Whenever you go from vertical to horizontal, it needs to be a wye fitting.


So you're saying that the piece used at the bottom of the toilet drain should be one of these:


07-16-2010, 04:09 PM
Here is one method wet venting the tub over the toilet.

07-16-2010, 04:58 PM
Hmm, I'm not really sure what to do with that, or how I could apply that to my situation.

07-16-2010, 09:28 PM
That's why a plumber on site would make all the difference.

Right now you have an unvented tub and toilet.
The toilet and the tub have the wrong fittings as they tie into the main run.
There is no way a plumbing inspector would pass that job as it sits.

07-17-2010, 06:19 AM
It appears you have a 4" line going to the septic tank, therefore, that cleanout opening you have in the "Y" should also be 4", not 3". The lack of a vent does NOT cause something to not drain, UNLESS there is also a more serious problem elsewhere. AAnd yes, the fitting should be the combination Y-1/8 bend you show.

07-17-2010, 12:08 PM
Adding a wye fitting wouldn't be a problem. I'm pretty sure all of the main line is 3 inch. I just need to figure out how to get this vented.

I should correct myself and say that the tub drained slowly, or slower than it should but it did drain.

Doherty Plumbing
07-17-2010, 09:14 PM
Adding a wye fitting wouldn't be a problem. I'm pretty sure all of the main line is 3 inch. I just need to figure out how to get this vented.

I should correct myself and say that the tub drained slowly, or slower than it should but it did drain.

The BEST way to replumb your house would be to have your sink tie into the drainage UPSTREAM of the toilet. This will give you no flat dry vents and would be sufficient vent for what you're doing (especially with 3" piping for the sink's wet vent). Ofcourse this is all up to local codes but what you would be creating is a simple wet vent for a bathroom group.

This may not fix the slow draining tub but it may certainly help.

Doherty Plumbing
07-17-2010, 09:25 PM
Similar to this.


07-17-2010, 10:26 PM
(especially with 3" piping for the sink's wet vent)

The sink isn't a 3 inch pipe, the toilet and what it connects to is, but the tub and sink drains are 2 inch I believe.

I'm sure there's a rag or something in the pipe, or again debris from a tub that's acted as storage for eighteen years.

I'll add one more photo of the floor plan of the bathroom from above, with the red lines indicating the current DWV, and the red X's indicating the vents, and the yellow lines indicating how the sink vent is tied into the other vent in the attic space.


If it would help anything I could easily use the access space where the plumbing for the tub is to run another vent. Basically the wall is usually closed off but at this time it is not, so I could easily run a 2 inch pipe all the way up to the attic and tie into the vent that isn't connected since there's already a hole in the roof for it.

I've always had luck in the past with DIY stuff here so I'm not sure what the issue is now, but even if you guys just offer suggestions it still gives me the power of being informed about things and in a better position not to be taken advantage of. If I can fix it myself great, but even if I can't I want to have an idea of what's going on.

Thanks again for any advice that steers me in the right direction.

Doherty Plumbing
07-17-2010, 10:36 PM
what I drew before still applies....

07-17-2010, 10:47 PM
It seems that venting is a popular subject in the forums today. I read through some of those threads and found advice very similar to yours. I'm just not that familiar with wet vents so I'm just wrapping my mind around it. I'm used to seeing waste goes down, vent goes up, just like the sink in my current setup. Thanks again for the suggestion.

07-17-2010, 11:22 PM
Just a couple of questions for clarification:

Can I still use this below the toilet:


This would allow me to add a cleanout.

Also, about the current vent that comes out of the roof: Would I need to go into the attic and cut the piece that goes into the wall and then elbow the sink vent into the roof vent, or could I just put a cap on the vent as it comes out of the bottom of the house?


Also, does anyone know of a list with images of the different types of DWV connections?

Wally Hays
07-18-2010, 06:12 AM
The concept is quite simple. The pipe serving as a wet vent is oversized to allow both waste and air to move in the pipe at the same time.