I have read many many posts about venting but still have a question.

I am adding a sink to an area that previously only had a toilet. ( I believe the room was a senior bedroom, we are adding the sink and enclosing the area to make a half bath)
During a previous plumbing inspection I was informed that the toilet was not vented and would have to be to pass.

Is it legal/possible to install the P-trap for the sink in the basement and run the vent parallel, and above the centerline of the drain before I head up and out?

I believe the requirements would be:
Max 24" drop from sink to trap
2" vent from drain through roof/soffit
Max 6' linear from center of each drain to center of vent.

I'll try to include a pic. Ignore the scale of the drawing and pipe I'm not an artist.

I don't see the commode in your drawing. You said the commode does not have a vent and since you are going to vent the commode to pass inspection you can just arm over to the sink (lavatory) if it is in the limits of the code in your area, in my area the arm can be 36 inches.

Ok, I guess a little more info is needed. The 3" to 4" drain on the left of the drawing represents the toilet. The connections that are there now are a mess of wye's and pipe that run at about a 50 degree angle (from horizontal) and then straight down about 4 feet to the main that is under the concrete. The inspector that was here said something like "Boy they sure left you a mess there". Very exciting for me to hear.

I'm not sure how to even run a vent off what is currently there. Since I'm adding the sink I figured the easiest way would be to wet vent the toilet through the sink drain.

Now to really complicate things, the wall that the sink is on is over the foundation and not accessible from the basement (the entire first joist space is over the foundation so I have no way to drill or connect the drain in that area) working in the joist space directly under the sink is my best option.

When you say 'arm over to the sink' do you mean a vent to the sink or the sink drain?

Can I vent the toilet and just run the sink drain to the toilet drain if the sink drain is under 6'?

SC:

I am not real clear here, but will attempt to answer your question. I am going to assume here that you have a 4" drain pipe for the toilet.

You need to cut a 4"x2" wye fitting into the toilet drain line within say... 6 feet or less...of the toilet elbow (no other fittings can be inbetween this wye and the toilet elbow). That 2" pipe then runs over to sink drain and stubs out 1.5" for the sink (stub out can be up to 6 feet away to sink), and then continues full size 2" out the roof or connects into another 2" vent elsewhere upstairs or in attic.

Hope that made sense. Let me know if need more. Mark

If this helped, please RATE THIS ANSWER. Thank you.

Thanks for the replies.

from the toilet flange there is a 45 dropping the drain from horizontal running left to right parallel to the front wall, then a wye with clean out maintaining the 45 pitch and turning the drain towards the center of the basement, then a wye with clean out dropping the drain to vertical where it connects to the main under the concrete. All of this is 3" pipe.

If what you have said still applies, I cut a 3"x2" wye into the first section of the toilet drain (which would point the 2" branch vertical) above that would be a 2"x1.5" tee. Running the 1.5 branch to the sink trap and the 2" up a bit more then routing back to the left around the toilet drain to the exterior wall up and out.

I think my original question still remains. Can I put the p trap for the sink in the basement?
and if the distance from the 2x1.5 tee to the p-trap is over 6' can I run the vent horizontal above the drain like in my original drawing?

In the picture that would make the yellow bits vent, the light blue sink drain, and the dark blue the wet vent. This is an elevation. The brown is the floor.

OK...Here is how I would do this:

3"x2' wye gets cut into 3" toilet drain line as you have it.

2" runs over to sink (no p-trap under floor), stubs out 1.5" using a 2" x 1.5" sanitary tee fitting at sink (p-trap here, under sink), and then 2" out the top of the sanitary tee fitting continues from there (at sink) full size 2" to connect into 2" vent or larger upstairs (or penetrate roof individually). Now you have a vented lavatory sink and WET vented toilet.

The reason you can't put p-trap in basement is because code will not allow a TAILPIECE (pipe from fixture to trap) to exceed 24" out of a p-trap... which your sink tailpiece will clearly exceed (never mind the 90s above floor as in your drawing). If exceeded 24" will get noises, gurgling and eventually bad smells from the inside of that pipe.

Anyway, that is my take on it... let us know what you think... Mark

Thanks Mark,

I was avoiding what you have been describing because I kept thinking I would have to bring the vent back to the toilet somehow. If the one 3x2 wye is all I need in the basement I can run the vent in a different wall.

1)The wall the sink will be on is an interior wall and doesn't run all the way to the roof. Is there a certain height I need to run above the sink before the vent turns horizontal?

2)from your description, I am assuming that there is no restriction on the length of the wet portion of the vent for the toilet. Correct?

HI SC:

1) Just take the vent off the top of the 2" x 1.5" sanitary tee and run the 2" vent anywhere you want to (connect to other 2" vent or larger, or out through roof by itself)... ;)

2) There is a distance vent to trap requirement for the wet vent, but you easily met that (distance from trap to vent, i.e. distance toilet to vent connection must not exceed 8-10 feet... your connection (the 3"x2" wye) is within 2 feet or so... so no issue here! ).

You sound like you get it just fine!

Keep us posted... Mark