Adding a utility sink to existing drain

[Chris Tjoumas]

Hi,

I have a bathroom that shares a wall with my garage. What I'd like to do is add a utility sink to my garage and I think I can tie into the drain my bathroom sink uses. My bathroom is on the main floor, so it drains into a pipe which you can see from the basement (picture attached). I'm assuming the vent is off of the same pipe and runs vertically up to the roof. I haven't opened the wall from the garage yet, so I'm just assuming and have attached a (very) crude picture (in black color) of what I'm guessing the vent is doing since there are no pipes in the garage. The red ink in the picture is what I think I can do using a double sanitary tee.

I live in Virginia so it seems from reading here while looking for an answer, pipes are much smaller here than on the west coast... the trap and drain for my bathroom sink are 1.5" PVC and tie into a 3" PVC which goes to the main drain line.

Hopefully this is enough info and the attached pictures help. Would my plan work using this double tee?

Thanks,
Chris

 

[Cacher_Chick]

You can install another wye downstream of the existing fixtures. The new sink will need its own vent.

 

[Sponsor]

 

[Chris Tjoumas]

I'm new to plumbing (I've done basic plumbing when remodeling bathrooms and kitchens, but never adding plumbing), so I'm not sure what would need to be done. When you say another wye would need to be installed downstream of the existing fixtures, do you mean even past where the shower and toilet connect to? Or, downstream of the existing vanity sink as I have annotated in black text on the attached image?

Doing a little research, I guess this is wet venting; does this annotation I have with the wye on the drain giving the new utility sink in the garage it's own drain/vent qualify for its own vent? I'll definitely need to check on my local codes, but I wanted to at least get the idea set.

Thanks again,
Chris

 

[Terry]

Only bathroom fixtures can be wet vented as a group. Since the garage sink or a washer doesn't fit in that group, it gets it's own vent and comes in downstream of the bathroom group.
This is what a plumbing inspector will tell you.

 

[Chris Tjoumas]

Ok, thanks. So, basically, I'd need to install a new PVC pipe that would run up the wall and outside of the roof as the new vent for the garage sink? And, if that's correct, then I would need to connect the drain of the garage sink downstream of the bathroom group, which would be basically somewhere in the middle of the two black straps you see in the picture?

I plan on getting this inspected so I know it's done right, but I just want to be sure I understand the requirements so I can plan the work.

Thanks,
Chris

 

[Terry]

Once you have vented the sink, it can tie back in at 42" above the floor.

 

[Chris Tjoumas]

Ok, so I can add a vent through the roof and from the bottom of that vent pipe, tie that into the drain line where my bathroom sink drains into? Sorry for the questions, but I just don't know enough about how everything should connect to fully understand it. I'm confused by the 42" above the floor comment - if I tie into the existing drain line the other sink is using, I assume the drain of that sink ties in about 42" above the floor, so I'm not sure where I'd tie the new sink drain pipe into. Earlier I thought the direction was to tie in downstream of the other bathroom fixtures, which I interpreted as drain past where the shower connects to (which was in between the black strap in the picture I attached; which is below the floor).

Chris

 

[Terry]

The waste line ties in downstream. The top side, the vent, can tie into another vent, if it's six inches above the flood level. In other words, six inches about the counter top. Most counters are 36" high, add six inches and you get 42".
Just so you know, most apprentice plumbers don't get to touch waste and vents for the first six months. We run water and get used to seeing how it's all run before they even start to explain it to us.

 

[Chris Tjoumas]

Thanks again, Terry. Ok, I think that makes sense. If I'm understanding it correctly, the new sink in the garage can tie into the vent stack which the current bathroom sink has coming up vertically from the drain as long as I'm 6" above flood level of the garage sink. A couple of questions:

• Does it matter where in the vent stack I tie into as long as it's 6" above flood level of the garage sink? I assume the vertical pipe above the drain of the vanity sink is the vent stack, but not sure if it ties into anything else further up the wall.
  
  
• For tying the drain of the garage sink into the waste line, is there any specific area where I need to tie into? Referring back to my picture from under the floor where the drain pipes are, if I understand "downstream" correctly, the sink drains first, then the toilet ties into that, then the last fixture which ties into that is the shower; would the garage sink tie in after the shower tie-in or could it be anywhere along that line?

Again, thanks for being patient as I'm trying to understand how to properly vent and drain this new garage sink. Once I understand the direction, I'll of course double check everything with my local codes and get an inspection setup.

Chris

 

[Cacher_Chick]

Sometimes it is easier to post a 3-D drawing of how you are thinking of doing it, and then people can comment from there. To explain everything in a way that everyone is sure to understand is harder.

 

[Chris Tjoumas]

Any recommendations on free software to put together a 3D drawing? I'd be happy to do that, but outside of the one picture I have where I've labeled the pipes, I don't know what else I can provide; I don't know what's behind the walls, so I would only be guessing the vent goes vertically up the wall and the drain is labeled in the one picture. But if you do not think that one picture is good enough, I can see about putting together a drawing.

 

[Chris Tjoumas]

Ok, attached is my best shot at this. I basically tried to mimic the image I have from underneath (in the basement) where I have the drain pipes labeled for the shower, toilet, and sink. I'm assuming the vent pipe goes up the wall behind the bathroom sink, so based on what Terry said earlier, I'd think about 42" from the floor, I'd tie into the pipe there to vent the new garage sink, and then tie the drain into some point further down, possibly a point past where the shower ties in. Not sure if this drawing helps or not.... again, all I can see are the pipes exposed from the unfinished basement - anything behind the walls I'm guessing.

 

[Cacher_Chick]

Sometimes it is easier to just get out a pencil and paper...

Cut out a section of the 3" drain line to install a new 3x3x2 wye to tie in your new sink drain. In the wall behind the new sink drain, install a new sanitary tee where the drain will go into the wall. Off the bottom of the sanitary tee you will be running 2" drain piping to your newly installed wye. Off the top of the sanitary tee will be the new vent going up. The vent can go straight up through the roof, or you can open up the wall above the existing sink to tie in the new vent to the existing vent. The connection of the new vent to the existing one should be made at least 42" above the floor.

 

[Chris Tjoumas]

Yea, I was thinking the same thing about drawing on paper Thank you for your response and the details! So it sounds like I can then cut into the 3" drain line anywhere between where the current sink and the toilet drain (so the order of draining would be current sink, new sink, toilet, shower...).

I will draw up what I understand, which sounds very clear, and post just to be sure. I may end up running a separate vent for the sink since I have access to the garage attic there, but not sure yet.

Thanks again!

 

[Reach4]

No p-trap for a toilet. The trap is built into the toilet.

 

[Cacher_Chick]

Yea, I was thinking the same thing about drawing on paper Thank you for your response and the details! So it sounds like I can then cut into the 3" drain line anywhere between where the current sink and the toilet drain (so the order of draining would be current sink, new sink, toilet, shower...).

Thanks again!

The new wye cut in for the new sink must be downstream of all of the bath fixture connections. Anywhere between the hangars in your photo would be fine.

 

[Chris Tjoumas]

I'm back - had a few other projects I needed to finish before getting to this.

I tried drawing on paper and i just can't get it right, but I think I see what needs to be done. Using my picture from the basement looking up at the plumbing, what I think it sounds like I can do is put a new wye into the larger drain that is downstream of the current bathroom sink, toilet, and shower. So, as you noted, cacher_chick, i would bring the drain through the first joist shown furthest to the right (this is the garage wall side) and into that pipe, which is shown between the two black straps helping to support. Is that correct?

Then as as Terry mentioned, i'd tie the vent to the existing vent stack the current sink is using, but make sure it's 6" above flood level (so it might be 42" off of the garage floor).

Does that sound right? If this isn't clear, I can try annotating again on that picture.. i just can't get a paper drawing to work out.

Thanks again!

Chris