Vent question
 

I'm moving a bathroom sink to a different wall and draining to existing 2" underfloor drain about 6' away. New drain pipe within wall will travel 18" horizontal, 18" vertical to area below floor, another 18" horizontal to connect to existing 2" drain with 1 1/2" vent. Can I use the existing vent? Or, do I have to install a new vent in the wall behind the new sink?

so its 36" from the lav? use a sanitary tee for the arm

Why would I need a sanitary tee if I'm going from the sink's trap to the existing waste line that already has a vent?

After the trap. the pipe goes horizontal. It has to hit a vent before dropping down to the drain below the floor. If not, it's considered an "s" trap which will, in most cases, cause problems with siphonage. Then you're house will stink and no one will want to visit!:thumbsup:

Thanks for the explanation. There is a 2" vent pipe for the toilet a few feet away in the same wall my sink will be located. Can I run a horizontal vent pipe into a tee attached to the toilet vent? I believe the horizontal vent pipe has to be 6-8" above the sink.

that would be fine,

it needs to be understood that the vent is not there to serve the drain, it is there to serve the trap

My next issue - or, maybe it's not a problem. I have to run the horizontal vent pipe through two 2 x 4 studs that are part of a weight bearing wall. (It's not the main weight bearing wall.) Any precautions, comments? There is no attic space for connection to the existing vent.

just posted today
http://www.diychatroom.com/f7/help-h...x-4-lbw-86793/

in my code, you have to vent within 3.5 feet on 1.5" pipe you can also use 180 degrees of turn. you'd be good in my state as long as the vent on the wc is at least 2"