Question for licensed plumbers

[MNBobcat]

Hi Guys,

I need to locate a vent pipe that I can tie into for adding a vent for a sink. I have found a pipe that looks to be either 1 1/4 or 1 1/2 inch located in a perfect spot. Yeah, I know...I'll look at it closer later to figure out the exact size. The pipe comes across the ceiling and then turns up through the ceiling passing through the floor above. It's likely going up through a wall cavity.

The problem is, I can't tell if its a drain or if its a vent. I know the best way to determine that is to try and trace the pipe but in this case I can't.

Are there any tricks of the trade to help identify what it is?

 

[RNeumann]

Turn on the faucets above one at a time to see if the line carries waste. You should be able to hear the water moving in the pipe- no mater what type of material it is.

What type of sink are you trying to vent? Where is it located (City, state not in the house). If you are in an area that is using the IRC instead of the UPC you have a few more options with regards to provent/mechanical vent/air admittance valve meaning you may not need to tie into anything.

 

[MNBobcat]

Thanks for the reply!

I'm in Minnesota which apparently uses the UPC. Minnesota doesn't allow Air-Admittance valves, unfortunately.

I have to install a commercial hand wash sink in the basement of my house. It's a 2-story home. I guess I could have the wife go around running water in all the sinks and tubs to see if I can hear water draining down that pipe. The most likely place would be the 2nd story bathroom since that's the only thing directly (2 floors) above.

 

[RNeumann]

You are sort of stuck. To be fully within code the line you need to tie into has to be a vent only line- no wet venting the basement sink. Hopefully when you run waste down the line it is only a vent.

If not, it’s going to be up to you how far you take this- forget code and do a air admittance valve, run a vent through the rim joist and up the exterior of the building or open drywall under a sink on the first floor and shoe horn a line into the vent just above the sink but below the countertop. Either of the second two would be to code.

 

[Steppenwolfe]

Can you put a studor vent under the sink? They work real well, and no need to vent to the outside.

 

[kenmac]

If you aren't going to have it inspected, Use an AAV and forget it

 

[quicksandfarmer]

To figure out whether the pipe is a drain or a vent, try and figure out what it might be venting (a fixture below it) or draining (a fixture above it). See if you can tell where the vent goes through the roof and where the drain exits the house. Generally you try to avoid long horizontal runs with DWV plumbing so it's most likely all in the same area.

PVC pipe is a good conductor of sound, sometimes you can have a helper tap on it and follow the sound.