2nd bathroom sink drain question

Hello,

Thanks to all who contribute to this forum.

I'm adding a second sink to create a double-sink bathroom and am not sure how to run the drain. At the spot where I'm adding the sink, there is a cast iron pipe running from the roof to the crawl space where it joins with the drains of a toilet, sink and tub, that are on the other side of the wall I'm working on.

Because of the wall studs it does not look like I can hook into the drain of the first sink (which is cast iron as well).

1. Do I hook the drain of this new 2nd sink into this cast iron vent / drain? If so, how? Two couplers and a PVC T?

2. An easier approach seems to be to run PVC down into the crawl space where I can hook into the cast iron pipe there. This is easier because a plumber had already replaced the tub drain with PVC with a rubber coupler to the cast iron pipe. So I can hook into the PVC part. The distance is about 3' down and 3' horizontally (sloped, of course).

I tried to read some code regulations but I'm not sure I understand them correctly.

Thank you in advance for all advice.

Ron

If I read you correctly, you've got two pipes running up. The one your sink is NOT connected to now is possibly the vent for those things below, so no, you should not use it as a drain. How to hook up to the existing one would depend on how things are layed out and the distances involved. Maybe a picture would help.

Thank you for the quick reply. It was just too late to get under the house to take a picture.

Yes the pipe I'm referring to is the vent so thank you for ruling that out. Here are the pictures above and below the house. The current sink is on the right and I'd like to add a second sink on the left, where the cast iron vent is. Running the water lines is not a problem. I just don't know how to do the drain. You can see that the PVC shower drain is just a few feet away from where my sink drain will be. Can I hook in to that?

Thank you in advance for all advice!