Venting two toilets with one vent, without gurgling

[user 32510]

Hello, I’ve searched a few forums but still haven’t found a good answer as to why my two toilets sharing one vent like to bubble and gurgle and splash when the other toilet is flushed. The two drain into one 3inch pipe as pictured. The center pipe is the vent pipe which connects to the original 4” cast iron pipe going through the roof.

There are no other venting problems anywhere in the house (anymore).

The main 4” cast iron pipe is leaking, so I would like to reconfigure the vent pipe while replacing the 20 feet of cast iron. ( I can use 3” S&D pipe all the way across the run right? Or should I use 4” due to the length before it hits the the cast iron underground pipe?)

So why does this cause gurgling and how might I be able to reconfigure it so it stops splashing water up the opposite toilet with every flush?

Thanks!

 

[Twowaxhack]

Because they’re connected to that cross fitting. Water shoots across the cross when one is flushed and will cause problems with the other one.

 

[user 32510]

Because they’re connected to that cross fitting. Water shoots across the cross when one is flushed and will cause problems with the other one.

That’s what I’ve been thinking for years. Would you say that just about any other configuration would solve this? I’m thinking about keeping the cross fitting there but having each toilet drain straight down to a 90-degree long sweep that flows right into the main pipe through Ys. Of course, with tee fittings still connecting to the cross for venting of each toilet.

The 2-inch pipe in the photo is what three sinks and two showers drain into. That’s what makes me wonder if I should stick to a 4-inch pipe from that point forward, like it has now, but the 3-inch pipe would still be a bottleneck at that point so I’m not sure if it would make a difference. For all I know, their internal diameters might be the same. I’m quite the noob when it comes to plumbing.


Any more thoughts?

Thanks for the reply!

 

[MicEd69]

Just replace the double Sanitary tee there with a double fixture fitting like this.

 

[breplum]

You should also be aware that the 90 degree elbow fittings, when carrying waste from vert. to horiz. must be long sweep fittings. None of yours appear to be. It is to help prevent clogging.

 

[Twowaxhack]

Just replace the double Sanitary tee there with a double fixture fitting like this.

View attachment 42270

I was just reading a post by Terry Love (rip) and he said that a double fixture fitting isn’t always good enough. You’d need a double wye and 1/8th bend AKA a double combination.

I’ve ran into problems with a sanitary cross like the posters pic shows here in this thread but it was with an existing home and the owners had the toilets installed by a flooring contractor. Nothing I could do, was on a slab. Of course they didn’t want to break up the floor.

We changed the toilets out to 2” flapper size and all was well.

I think if I did the work after reading what Terry Love said, I wouldn’t use the double fixture fitting. He was a pretty good plumber so I believe his experience.
You can read this entire thread.
https://terrylove.com/forums/index.php?threads/back-to-back-toilet-installation.33720/
The double fixture fitting may very well work in some configurations but maybe not all. I suppose it may depend on pipe size and how much pipe is between the double fixture fitting and the 90 directly under the toilet transitioning from vertical to horizontal .

In a true back to back toilet installation you wouldn’t have much of any pipe between the fixture fitting and the 90. I had trouble doing it with a double combination and had to use a double wye. It’s been a thing in commercial installs for the direct flushvalves.

 

[user 32510]

You should also be aware that the 90 degree elbow fittings, when carrying waste from vert. to horiz. must be long sweep fittings. None of yours appear to be. It is to help prevent clogging.

Thanks for the advice! I do plan to use long sweep elbows or long sweep tees when I get to this project in a couple weeks.

So when using a 90-deg elbow going from horizontal to horizontal, would you still use a long sweep or just use a normal 90? I’ll be installing one of those too. It’s currently a straight shot across my crawl space from that pictured junction to the main line that goes underground but I would like the new pipe to follow the wall to the corner, turn 90 degrees then straight down through a ling sweep tee so I can put a cleanout cap on “top” of the tee.

Thanks again

 

[user 32510]

I was just reading a post by Terry Love (rip) and he said that a double fixture fitting isn’t always good enough. You’d need a double wye and 1/8th bend AKA a double combination.

I’ve ran into problems with a sanitary cross like the posters pic shows here in this thread but it was with an existing home and the owners had the toilets installed by a flooring contractor. Nothing I could do, was on a slab. Of course they didn’t want to break up the floor.

We changed the toilets out to 2” flapper size and all was well.

I think if I did the work after reading what Terry Love said, I wouldn’t use the double fixture fitting. He was a pretty good plumber so I believe his experience.
You can read this entire thread.
https://terrylove.com/forums/index.php?threads/back-to-back-toilet-installation.33720/
The double fixture fitting may very well work in some configurations but maybe not all. I suppose it may depend on pipe size and how much pipe is between the double fixture fitting and the 90 directly under the toilet transitioning from vertical to horizontal .

In a true back to back toilet installation you wouldn’t have much of any pipe between the fixture fitting and the 90. I had trouble doing it with a double combination and had to use a double wye. It’s been a thing in commercial installs for the direct flushvalves.

That’s a great thread! Thanks for sharing it. And your own experience as well.

I wish I could go with a double wye and a couple of 45s but I will have to redo the whole shebang to be able to locate a double wye low enough. The other thought I had was If I do decide to do the whole shebang, I’ll leave the current double tee in place along with the current reducing tee for the 2-inch pipe. Then replace the 90 at the bottom with a long sweep tee while adding two more long sweep tees for three in a row. I’d cap the open end with a cleanout cap. And I’d add a tee just below each toilet to tee off to the current double tee for venting of each toilet. Trying to fit all of those pieces together might be a bit of a challenge but it would make me feel better than trying a double fixture tee just to find out that the real problem is the proximity of the toilets and even a double fixture tee would retain at least some of the gurgling.

Thanks for all of the replies! I’m surprised to get this much response amd I appreciate you all.

 

[MicEd69]

That’s a great thread! Thanks for sharing it. And your own experience as well.

I wish I could go with a double wye and a couple of 45s but I will have to redo the whole shebang to be able to locate a double wye low enough. The other thought I had was If I do decide to do the whole shebang, I’ll leave the current double tee in place along with the current reducing tee for the 2-inch pipe. Then replace the 90 at the bottom with a long sweep tee while adding two more long sweep tees for three in a row. I’d cap the open end with a cleanout cap. And I’d add a tee just below each toilet to tee off to the current double tee for venting of each toilet. Trying to fit all of those pieces together might be a bit of a challenge but it would make me feel better than trying a double fixture tee just to find out that the real problem is the proximity of the toilets and even a double fixture tee would retain at least some of the gurgling.

Thanks for all of the replies! I’m surprised to get this much response amd I appreciate you all.

I'm wondering if you could simply use the double fixture fitting in place of the double sanitary tee, as that sometimes works just fine, but then as a safety, install a redundant vent between the toilet on the right and the double fixture fitting. I don't think you would need a "safety vent" on both toilet drains. That would be a better sewer flow than what you describe above.

And while there is HUGE debate on using Sanitary tees on their back for vent connections, using them here as just a "safety vent" might be reasonable. I think you would be able to snake a 1 1/2" vent line back to the main vent if you used a reducing street sanitary tee. A combo fitting might even be able to get in there as well.

Twowaxhack, what do you think?

 

[Twowaxhack]

The vent isn’t the issue, it’s the actual water shooting across the fitting.

He could easily use a double combo that would stop the possibility and it would fit fine.

I just talked a customer out of a Toto Drake because of the possibility of this issue. She has back to back toilets. We decided to install a regular 2” flapper 1.6 gpf toilet.

 

[user 32510]

This did the trick! I opted for the double wye because it was cheaper and seemed safer over the double fixture connector since I could still look through one side of the double fixture and see through the other inlet.

Thanks again for everyone’s input!

One thing I haven't mentioned is that I have 3" flappers in both toilets, so this works even with the 3-inchers.

 

[Twowaxhack]

All those tees on their backs and 90’s makes my skin crawl. It looks like a vent and it’s back pitched, I’m sure it’s holding water. Looks like a long horizontal vent below all the fixtures in the house. Terrible improper design.

Your new work looks good to correct your toilet crossover.

 

[user 32510]

Yes, the more I learn about plumbing the more I see wrong with what was done before I bought the house.

I think there must be some water being held in the 2" pipe just before it meets the 3".

Once I learned about the tees on their backs, I rethought what I had planned to do here. I've learned a lot on this little project. Let me know if you guys see anything else of concern and if any more work needs to be done in the future, I'll be sure to redo things correctly.

 

[MicEd69]

Twowaxhack is right I'm afraid. See below.

 

[user 32510]

I may redo that whole manifold section someday, but for now it seems to be working and I'm not subject to any inspections anytime soon. I may need to pull that plug off the end of the 2" pipe to be sure no debris is collecting where the sanitary tees are on their backs. The slope on that two-inch section looks wrong to me too, but I haven't put a level on it to be sure. At this point, I'm probably going to wait for problems to develop and then get my tools back out and go back to work on the 2" sections. That horizontal rubber connector is also a concern of mine. I'm sure it will someday start leaking.