I plan to add a bar sink next to the bathroom in my office. The horizontal distance from the tailpiece of the new sink is about 54” from the P-trap outlet of the existing bathroom sink. I am trying to connect my new sink to the existing vent (of the bathroom sink). I was told that the maximum horizontal distance from the P-trap to vent is 36”. Rather than placing the new P-trap right underneath the new sink, can I place the P-trap between the new sink and existing vent, say 18” away from the new sink tailpiece and 36” away from the existing vent? Thanks for anyone's help.

Trap-to-Vent distances are mandated by local Plumbing Codes and vary depending on Plumbing Code you fall under. For example: According to "2006 International Plumbing Code" you should be OK with being 54" away from vent no mater what size your trap is. ( See the enclosed tables ). However, what you are describing is installing "Running Trap". These traps are not allowed in my area. Hope that answers your question. Back to you. Milo

Thanks. A city building inspector told me that the distance between trap and vent cannot exceed 3 feet. I am also at S. California. Are you saying that in California the "running trap" is not allowed?

Yes, I am in So.California as well. We fall under UPC. The UPC allows an unvented 1-1/2" fixture arm to run 3' 6" ( 42" ) from trap to vent. However, there are some incorporated cities in So.California, like Burbank, Inglewood or Laguna Beach that have additional Code requirements that supersede general Unified Plumbing Code.

I cannot find any specific mention about "running trap" in UPC in residential application and I have never seen one installed in So.California. However, I know that - let's say in San Juan Capistrano, running traps with 1 (one) clean out on each side of the trap, are required in commercial installations where grease interceptors are present. Other than that, running traps are mostly used in grey water systems.

If you want to install running trap because your sink is too far away from the wall so I can almost guarantee you Inspector is not going to allow it. I suggest that you call a plumber who will solve this situation for you. There is always a way to do it.

But since Inspector is the one who signs off the Inspection Card than I would do what he asks me to do. Otherwise, you are asking for trouble. If this job was being done w/o permits, than you could use Air Admittance Vent. That would solve your problem in 2 seconds.

Question: What City are you in ?

Back to you. Milo

Thanks a lot. I am in City of San Gabriel and it is for my office.