How to tie in a back-to-back sink to an existing horizontal drain line?

[Plumber01]

But I don't see that language as requiring that the tee be upside down.

The language is right there in 905.1. Connected to drip back by gravity to the drainage pipe it serves.

UPC, IPC, ABC, whatever. Every plumbing apprentice is taught to install them upside down. It is taught in apprenticeship classes, its drawn that way in the illustrated training manual, its drawn that way on the journeyman test, its drawn that way on engineered blueprints.

Should we start installing a wye+eighth bend, rolled at a 45 degree angle above centerline on a horizontal trap arm backwards because air doesn't know up from down? No. Because we always want a potential sewage backup, or perhaps, a vent turned into a drain via wet vent to drain downstream with gravity.

It may not be significant in this context, but don't you think we should show DIYers the correct way to do it?

 

[wwhitney]

The language is right there in 905.1. Connected to drip back by gravity to the drainage pipe it serves.

So I think what we're discussing is just the orientation of the san-tee, and for the short horizontal length of the side inlet, which way that little area will drip back by gravity. Because either way it drains, it's just a question of whether the division point between draining to the vertical vent or draining to the horizontal vent occurs directly at the sidewall of the vertical vent, or occurs an inch or two to the right at the side edge of the san-tee fitting.

I hope we can agree that performance wise, it absolutely doesn't matter. If that area gets filled with water due to a clog or a test, it's going to drain out unimpeded either way. Unlike your horizontally reversed combo example, where the reversed direction would clearly impede drainage.

As to code language, IPC allows both options. On reflection, I'm going to agree with you that the UPC requires the san-tee to be upside down. Because the language is not just "graded to . . . " but "graded and connected to . . ." So the word connected is there to dictate the orientation of the connector, i.e. the san-tee.

But I will say that any inspector who calls that as a violation and requires the san-tee to be cut out and reinstalled upside down is wasting everyone's time. Because there is zero performance benefit.

Cheers, Wayne

 

[Sponsor]

 

[Jeff H Young]

A young kid new to trade would be told how to do it. a seasoned journeyman would never ever vent this way unless he had a brainfart and installed it wrong (that happens) but Ive never heard or seen this intentionally done . However if they are illegally wet venting between floors as I suspect maybe it would be better to install santee wrong as well. you wouldn't want soil and paper coming down and catching on the vent

 

[wwhitney]

A young kid new to trade would be told how to do it.

I guess that's my issue with this discussion--there's a difference between (A) "that's how I was taught to do it," (B) what will perform well, and (C) what the codes requires. Of those, only (B) and (C) matter to me, there are plenty of examples in the various trades of traditions that get passed along but have no performance or code justification. Ideally (C) is based only on (B), but unfortunately there are examples where (A) has been incorporated in the code. I think this question is one example of that in the UPC.

Cheers, Wayne

 

[Jeff H Young]

In my world really only plumbing in southern California its how everyone learns how to do it. A upside down santee will get attention . I do appreciate input and this forum because it allows others opinion and ways of doing things some because of codes, some based on misinformation that gets passed on, and some that is incorrect .
I would like to know why there is a 3 inch line going up the wall though to know if he needs to address the way this is plumbed though You don't just run a 3 inch stack up for nothing

 

[Terry]

Wet venting is same floor, bathroom fixtures only. No kitchen sinks, washers or laundry trays.

If that 3" pipe is serving a bathroom above, then no vent can tie into it on the floor below. The vent needs to tie in above the flood level of the fixtures one the next floor up. Or find another way to vent the fixtures in the basement.

A santee used in venting is turned upside down to allow water to drain out.

 

[wwhitney]

A santee used in venting is turned upside down to allow water to drain out.

Water is going to drain out with either orientation. It's just a question of which way it drains out, whether it's OK for that little inch or two in the side branch to drain out the bottom of the san-tee instead of out the side branch. Which makes zero difference in practice.

Although, maybe I'm missing something here. I don't have any plastic san-tees on hand at the moment and didn't happen to experiment when I was gluing them up most recently. I'm assuming that when you glue a pipe into the side branch, if the through path is dead plumb, you can achieve 2% slope towards the san-tee, level, or 2% slope away from the san-tee, all with relative ease. I.e. the san-tee orientation doesn't restrict you on the pipe slope.

If I'm mistaken, if with the usual orientation on a plumb san-tee it's really hard to get the pipe coming in the side to be level or slope away from the san-tee, then I agree that's a violation of UPC 905.1 when used for vents. Not the san-tee orientation per se so much as the resulting slope on the vent pipe coming in.

Can anybody clarify this point? Thanks.

Cheers, Wayne

 

[Terry]

This is how I install a santee on a vent line.

And how I install it for a sink.

 

[oldandslow]

Once again, I appreciate all the information - I've learned a lot about plumbing! I've also learned that I don't need a utility sink that badly - the bucket and hose in the backyard will continue do just fine for washing paint brushes, etc.

I won't do a project "wrong", but I'm also not going to tear out the existing plumbing that is working just fine, to code or not. And I'm certainly not going to tackle a 3" drain stack for my first DWV project!

To close the loop on some of your questions or speculations:

• The house is about 30 years old
• The basement bathroom was there when I bought the house 5 years ago
• The aforementioned lav, a stall shower, and a toilet where already there
• There's no evidence the concrete was jackhammered and re-poured, so I assume the toilet was original construction
• I don't know if the sink was original or added later - from some of your comments it may have been the latter
• I'm pretty sure the 3" stack is wet, since there's a powder room directly above it
• I haven't experienced any plumbing problems with the house (so far, knock on wood!)

Thanks again,
Rob

 

[Jeff H Young]

Ok well if you ever decide to do some plumbing work and bring it up to code your main issue would be the vent. and to fix that would be minimal almost anything will work in plumbing using wrong fittings , pipes too small, if pipes have grade they are going to drain, You can get away with a lot , so not surprising that the lav works fine. I run into things almost daily that are hacked and some work fine. The codes are meant to make things work to a greater degree of certainty I believe.
I had a feeling that vent had to be tied into a 3 inch waste stack. Not the kind of thing that would pass here. Something I've never done, So kind of hard to advise that its just fine the way it is. But not surprising though .
Good luck on next project!