Author Topic: Tying sink drain into 3" toilet wet vent  (Read 565 times)

J Boogie

  • Pencil Stache
  • ****
  • Posts: 749
Tying sink drain into 3" toilet wet vent
« on: September 24, 2018, 11:03:22 AM »
Anyone here familiar with wet venting and loop venting?

Remodeling my bathroom and I switched to a wall mounted sink. The previous drain went into the wall on the side, which was vented. I want to run the P trap straight back into the wall with the supply lines and tie it into the 3" toilet drain which is a wet vent.

Unfortunately, it is generally forbidden by most building codes to tie into a wet vent if you are downstream of the toilet drain. Can I disregard this? I have pulled no permits and have no compelling reason to meet code if it is not based on sound reasoning.

Consider the following from Plumbing and Mechanical magazine:

"The most commonly added requirement is that the water closet must be the last fixture in the wet-vented system. That makes it difficult for a double bathroom group wet vent. The two water closets would have to tie in together.

Actually, there is no technical justification for making the water closet the last fixture. Thousands of wet-vented systems are working where the water closet is not the last fixture. Someone assumed the water closet is a blow-out fixture that blasts through the pipe, sucking everything with it. Well, that isn’t true."

So if you do believe this is a legitimate rule, is this still bad to tie into this drain if I loop vent (or AAV) my sink drain?


Jon Bon

  • Pencil Stache
  • ****
  • Posts: 567
  • Location: Midwest
Re: Tying sink drain into 3" toilet wet vent
« Reply #1 on: September 24, 2018, 12:21:50 PM »
I dont think I understand completely what you are trying to do.... However that will not stop me from telling you what you should do!

I think you will be fine. a 1.5 inch line into the toilet line? The toilet works fine right now? I dont think it would even notice a bathroom sink draining into it.

Papa bear

  • Pencil Stache
  • ****
  • Posts: 781
  • Location: Ohio
Re: Tying sink drain into 3" toilet wet vent
« Reply #2 on: September 24, 2018, 01:05:37 PM »
I’m not a plumber, but have worked with some wet vents and installed some.

So you want to tie your sink drain into the vent for the toilet, making this a wet vent, correct? As in currently there is just a vent and no drain?

If that’s what you’re going with, I was cautioned about shit backing up into the sink. I would imagine it would all work fine though.




Sent from my iPhone using Tapatalk

J Boogie

  • Pencil Stache
  • ****
  • Posts: 749
Re: Tying sink drain into 3" toilet wet vent
« Reply #3 on: September 24, 2018, 01:39:17 PM »
I’m not a plumber, but have worked with some wet vents and installed some.

So you want to tie your sink drain into the vent for the toilet, making this a wet vent, correct? As in currently there is just a vent and no drain?

If that’s what you’re going with, I was cautioned about shit backing up into the sink. I would imagine it would all work fine though.




Sent from my iPhone using Tapatalk

Sorry for the confusion Jon Bon and Papa Bear.

Here are some diagrams which should explain things better.

I am not concerned so much about things backing up, or even the glug-glug-glug that occurs in the absence of a vented drain, but concerned about potential siphoning from the sink's P trap caused by the toilet which is considered by some to be a "blow out fixture" which has the potential to make such a forceful journey down the drain that it occupies the entire 3" worth of drain pipe as it passes by the wye tee I'll use to tie the sink line in and sucks (siphons) the water from the upstream P trap.

Whew. Typing that out, it sounds completely unlikely that it could happen. Are there any other potential issues I'm not considering?

J Boogie

  • Pencil Stache
  • ****
  • Posts: 749
Re: Tying sink drain into 3" toilet wet vent
« Reply #4 on: September 24, 2018, 01:54:34 PM »
I guess I could tie it in and then check the clean out in my sink's trap after flushing to see if siphoning has occurred, I could measure the before and after qty of water in the trap.

Papa bear

  • Pencil Stache
  • ****
  • Posts: 781
  • Location: Ohio
Re: Tying sink drain into 3" toilet wet vent
« Reply #5 on: September 24, 2018, 02:10:14 PM »
Yeah, the only thing I would see there is having the p-trap siphon out the water, as you suggested.  An AAV would probably work above the trap if it is a problem.


Sent from my iPhone using Tapatalk

BDWW

  • Bristles
  • ***
  • Posts: 416
  • Location: MT
Re: Tying sink drain into 3" toilet wet vent
« Reply #6 on: September 24, 2018, 02:44:54 PM »
The siphoning can be a problem. I've done it before and regretted it. In my case, it siphoned water out of the trap, and then I was getting sewer gas venting into the house (eww, wife was not pleased with the smell).

I kept it, but added a deeper trap in the hopes it wouldn't be able to pull enough pressure to empty the trap. Seems to be working so far.

J Boogie

  • Pencil Stache
  • ****
  • Posts: 749
Re: Tying sink drain into 3" toilet wet vent
« Reply #7 on: September 24, 2018, 03:15:49 PM »
The siphoning can be a problem. I've done it before and regretted it. In my case, it siphoned water out of the trap, and then I was getting sewer gas venting into the house (eww, wife was not pleased with the smell).

I kept it, but added a deeper trap in the hopes it wouldn't be able to pull enough pressure to empty the trap. Seems to be working so far.


Interesting. Does it go pretty much the same as the image I attached? Do you have a 3" wet vent? How long of a run is the vent? What GPF is your toilet?

At this point I'm hesitant to put an AAV in a wall without an access panel so I'm thinking of running a loop vent in the wall.

Jon Bon

  • Pencil Stache
  • ****
  • Posts: 567
  • Location: Midwest
Re: Tying sink drain into 3" toilet wet vent
« Reply #8 on: September 24, 2018, 04:14:44 PM »
Yeah just put in an autovent, costs 30 bucks at lowes.

Papa bear

  • Pencil Stache
  • ****
  • Posts: 781
  • Location: Ohio
Re: Tying sink drain into 3" toilet wet vent
« Reply #9 on: September 24, 2018, 04:37:02 PM »
Yeah just put in an autovent, costs 30 bucks at lowes.

I see OP’s problem. It’s wall mounted, so the trap and waste are behind the wall.  You would need to have a wall vent in the drywall for the AAV to work and allow in air.

Best idea is to hard pipe vent it back into the main stack as done before. 

So the 3” toilet line will have a wet vent from the sink and then another vent where the old sink waste line was previously.  That shouldn’t be a problem.


Sent from my iPhone using Tapatalk

J Boogie

  • Pencil Stache
  • ****
  • Posts: 749
Re: Tying sink drain into 3" toilet wet vent
« Reply #10 on: September 25, 2018, 08:45:43 AM »
So, this pic should explain a little better how I would rather not tie into the previous vented drain.

Due to the strange sideways stud situation, I don't have enough material leftover after hogging out room for a 1 1/2" drain.

I also don't want to run my P trap sideways into the wall, or run drain pipe (even a nice chrome pipe) back and around the corner on the outside of the wall.

In my next post I'll propose a couple ideas.

J Boogie

  • Pencil Stache
  • ****
  • Posts: 749
Re: Tying sink drain into 3" toilet wet vent
« Reply #11 on: September 25, 2018, 08:53:20 AM »
Ok, so here's my first idea. To prevent my sink's P trap from being siphoned, I can tie the sink drain into the vent pipe - which means if there is any negative air pressure (sucking) on the sink drain, it can pull air from the vent pipe instead of exerting negative pressure on the sink's P trap.

J Boogie

  • Pencil Stache
  • ****
  • Posts: 749
Re: Tying sink drain into 3" toilet wet vent
« Reply #12 on: September 25, 2018, 08:56:45 AM »
And here's my second, utilizing a loop which I believe is not needed given the sink is draining into a wet vent. I am reluctant to do this given how little space I have in my wall cavity, but if it's needed then I'll find a way.

AccidentalMiser

  • Pencil Stache
  • ****
  • Posts: 632
Re: Tying sink drain into 3" toilet wet vent
« Reply #13 on: September 25, 2018, 09:09:57 AM »
Can you go up through the ceiling and tie into the vent pipe in the attic or is this the first floor of a multi-story structure.

Have you posted on terrylove.com?  They’ll abuse the shit out of you but you’ll get good answers and won’t have sewer gas coming back through the siphoned sink trap.

Your “first idea” to tie the sink drain into the vent pipe is what you’re supposed to do unless I’m not understanding.

J Boogie

  • Pencil Stache
  • ****
  • Posts: 749
Re: Tying sink drain into 3" toilet wet vent
« Reply #14 on: September 25, 2018, 10:03:05 AM »
Can you go up through the ceiling and tie into the vent pipe in the attic or is this the first floor of a multi-story structure.

Have you posted on terrylove.com?  They’ll abuse the shit out of you but you’ll get good answers and won’t have sewer gas coming back through the siphoned sink trap.

Your “first idea” to tie the sink drain into the vent pipe is what you’re supposed to do unless I’m not understanding.

It's the first floor. After searches I definitely end up on the terry love and john bridge and fine homebuilding forums, just haven't registered at any of those places. I'm a single forum user I guess.

Thanks for the feedback! I think my first idea is all I need as well. If I wasn't draining into a wet vent, then I think I would need a loop - but as far as I can tell here, no loop should be needed. Also, not sure if it's relevant but the sink will not be pluggable (though it is conceivable that it could clog at some point).

robartsd

  • Handlebar Stache
  • *****
  • Posts: 1874
  • Location: Northern California
Re: Tying sink drain into 3" toilet wet vent
« Reply #15 on: September 25, 2018, 11:14:04 AM »
Here are some diagrams which should explain things better.

I am not concerned so much about things backing up, or even the glug-glug-glug that occurs in the absence of a vented drain, but concerned about potential siphoning from the sink's P trap caused by the toilet which is considered by some to be a "blow out fixture" which has the potential to make such a forceful journey down the drain that it occupies the entire 3" worth of drain pipe as it passes by the wye tee I'll use to tie the sink line in and sucks (siphons) the water from the upstream P trap.

Whew. Typing that out, it sounds completely unlikely that it could happen. Are there any other potential issues I'm not considering?
Glug-glug-glug is the sound of the siphoning happening. The saving grace of this system is that every toilet flush should be followed by use of the sink providing a renewal to the sink's P trap. If the sink did get plugged the discharge from draining the full sink could also cause a siphoning.

Personally, I'd prefer to use a 1 1/2" drain pipe to the 3" toilet drain line as you propose, but route a 3/4" vent pipe up from the sink to the stack vent. While 3/4" vent for the sink is not the proper vent size for the new sink drain to count as a wet vent for the toilet, the toilet's venting requirement are already met with existing pipe. Is there a way to route a 3/4" vent passed the problem studs?

J Boogie

  • Pencil Stache
  • ****
  • Posts: 749
Re: Tying sink drain into 3" toilet wet vent
« Reply #16 on: September 25, 2018, 12:05:31 PM »
Here are some diagrams which should explain things better.

I am not concerned so much about things backing up, or even the glug-glug-glug that occurs in the absence of a vented drain, but concerned about potential siphoning from the sink's P trap caused by the toilet which is considered by some to be a "blow out fixture" which has the potential to make such a forceful journey down the drain that it occupies the entire 3" worth of drain pipe as it passes by the wye tee I'll use to tie the sink line in and sucks (siphons) the water from the upstream P trap.

Whew. Typing that out, it sounds completely unlikely that it could happen. Are there any other potential issues I'm not considering?
Glug-glug-glug is the sound of the siphoning happening. The saving grace of this system is that every toilet flush should be followed by use of the sink providing a renewal to the sink's P trap. If the sink did get plugged the discharge from draining the full sink could also cause a siphoning.

Personally, I'd prefer to use a 1 1/2" drain pipe to the 3" toilet drain line as you propose, but route a 3/4" vent pipe up from the sink to the stack vent. While 3/4" vent for the sink is not the proper vent size for the new sink drain to count as a wet vent for the toilet, the toilet's venting requirement are already met with existing pipe. Is there a way to route a 3/4" vent passed the problem studs?

That crossed my mind, I think a 3/4 vent could make its way through.  I'll probably get a nice long spade bit and see what I can do.

Inspectors/Buttoned up Pros would probably balk at using 3/4 pipe back here but begrudgingly admit it's mechanically sound.