Odd drain routing, input wanted

[plumb_bum]

Edit: apologies for the duplicate posts, it was held up in moderation and I didn't realize it.

We are replacing the tub and I noticed something odd about the drain coming off the bathroom sink. It takes an indirect path to the main 3" line. It drains into a 2" or 2.5" line that runs parallel to the main 3" line before looping back around the end of the 3" before joining via wye. See attached photos for clarity.

Wanted to get thoughts as to why they might have done it this way. In my non-plumber mind I assume connecting to the main 3" line via combo wye would make the most sense, both in terms of flow and job efficiency. Would that have caused drainage issues or is there a code restriction that prevents such routing?

 

[wwhitney]

Assuming the only dry vent is at the lavatory, and the other 2" line is the tub, then the DWV is set up so that the lav hits the tub first to wet vent it, and the combined drain hits the WC to wet vent it.

Some plumbing codes, such as the UPC, require that the WC be the downstream-most wet vented fixture as was done here. The unamended IPC does not require that.

Cheers, Wayne

 

[Sponsor]

 

[plumb_bum]

Assuming the only dry vent is at the lavatory, and the other 2" line is the tub, then the DWV is set up so that the lav hits the tub first to wet vent it, and the combined drain hits the WC to wet vent it.

Some plumbing codes, such as the UPC, require that the WC be the downstream-most wet vented fixture as was done here. The unamended IPC does not require that.

Cheers, Wayne

That makes sense and you are correct, the dry vent is off the lavatory and it would hit the tub first based on the current configuration

I was thinking of moving the toilet over a couple inches as well, but now I might just use an offset flange and leave the routing alone.

 

[wwhitney]

What plumbing code are you under, or what state are you in? If it's the IPC, you likely could remove the constraint of having the WC last on the wet vent if you want to reconfigure the DWV.

Cheers, Wayne

 

[plumb_bum]

What plumbing code are you under, or what state are you in? If it's the IPC, you likely could remove the constraint of having the WC last on the wet vent if you want to reconfigure the DWV.

Cheers, Wayne

I'm in Georgia which I believe falls under the IPC with GA specific amendments- https://dca.georgia.gov/document/document/ipc-2026-amendment-packet-2024-edition/download

I'm wary to mess with the venting as I haven't had any issues with drainage and would hate to "fix it till its broken". Would I be tempting fate to reconfigure?

I believe these GA amendments are the most applicable, but neither fit so it looks like their isn't a specific local code on the topic.

SECTION 913
WASTE STACK VENT
*Revise Section 913.2 ‘Stack installation’ to read as follows:
913.2 Stack installation. The waste stack shall be vertical. Fixture drains shall connect separately
to the waste stack. The stack shall not receive the discharge of water closets or urinals.
(Effective January 1, 2026)

SECTION 914
CIRCUIT VENTING
*Revise Section 914.2 ‘Vent connection’ to read as follows:
914.2 Vent connection. The circuit vent connection shall be located between the two most
upstream fixture drains. The vent shall connect to the horizontal branch and shall be installed in
accordance with Section 905. The circuit vent may receive waste discharge from fixtures located
within the same branch interval, provided that the wet portion remains the same size as the
horizontal branch.
(Effective January 1, 2026)

 

[Reach4]

You are not doing section 913 stack or 909 circuit venting.

Horizontal Wet Venting method is located in Section 912

 

[plumb_bum]

You are not doing section 913 stack or 909 circuit venting.

Horizontal Wet Venting method is located in Section 912

correct, the GA specific amendments have nothing additional for that section. The only sections they amend in chapter 9 are 903, 911, and 913.

What are your thoughts on redoing the dwv or keeping it simple and using 1.5" offset flange? There is a joist under the WC so realistically I think the most I could get out of it is 2", maybe 3". Don't think the juice is worth the squeeze.

 

[Jeff H Young]

why isnt moving a toilet a few inches ? if not dont move it but nothing wrong with whats there as far as a desire to replumb it, besides it looks like a sensible routing .
I guess you are talking about cutting off the closet bend and putting it closer to the joist , sounds reasonable if you want it there

 

[Reach4]

Looks right to me, except your PVC to ABS transition joint would appear to be in violation of Section 705.16.4 of IPC. I would not bother changing it.

705.16.4 Plastic pipe or tubing to other piping material.
Joints between different types of plastic pipe shall be made with an approved adapter fitting, or by a solvent cement joint only where a single joint is made between ABS and PVC pipes at the end of a building drainage pipe and the beginning of a building sewer pipe using a solvent cement complying with ASTM D3138. Joints between plastic pipe and other piping material shall be made with an approved adapter fitting.
Joints between plastic pipe and cast-iron hub pipe shall be made by a caulked joint or a mechanical compression joint.

 

[plumb_bum]

why isnt moving a toilet a few inches ? if not dont move it but nothing wrong with whats there as far as a desire to replumb it, besides it looks like a sensible routing .
I guess you are talking about cutting off the closet bend and putting it closer to the joist , sounds reasonable if you want it there

Replacing the tub and had to pull toilet to get make room for the tub. Since it is out we thought about kicking it closer to the vanity and further from tub, maintaining the minimum 15". I don't want to go on the other side of the joist as that would probably be a tad close to the vanity at that point.

Looks right to me, except your PVC to ABS transition joint would appear to be in violation of Section 705.16.4 of IPC. I would not bother changing it.

That was done by a plumber several years ago, the previous flange failed, water leaking into the garage. I didn't have time to tackle it myself at the time and paid to have it fixed. Older home piped with ABS and no one really uses ABS in this area anymore, every plumber wants to come in with PVC. I can source ABS pipe and fittings from one of the local big box stores, they keep a small selection on hand, enough for my needs.

 

[Reach4]

I am not following exactly what you want to do with the toilet position, but a couple comments.
1. If you have enough room, a shielded flex coupling is the approved way to transition from ABS to PVC. I would not change unless part of another change.
2. Offset flanges can be really good, and will let you rotate the position of the flange 1.5 inch in any direction.
https://www.supplyhouse.com/Sioux-Chief-889-AOM-3-x-4-Full-Flush-889-Series-Offset-Closet-Flange is the ABS version, and
889-POM is PVC. https://www.homedepot.com/p/Oatey-3...ge-with-Stainless-Steel-Ring-436062/303826505 is out of stock. https://www.homedepot.com/p/JONES-S...or-4-in-Schedule-40-DWV-Pipe-C58434/315676103 can be ordered.

https://www.homedepot.com/p/JONES-S...r-Cast-Iron-or-Plastic-Pipe-C40-320/100168417 has a 1 inch offset, but I suspect it is more likely to interfere with a joist. It is wider I am thinking. If you try it out, you might post some dimensions for the next person who might consider it. The 2 inch part of the description may be how far down it goes, but I don't know where they are measuring to.

Some offset flanges have been notoriously bad. These are good.

 

[Jeff H Young]

how many inches do you want ? cut the 90 off glue another one on use a offset if you have to , worse case head out that joist no biggie

 

[plumb_bum]

I am not following exactly what you want to do with the toilet position, but a couple comments.
1. If you have enough room, a shielded flex coupling is the approved way to transition from ABS to PVC. I would not change unless part of another change.
2. Offset flanges can be really good, and will let you rotate the position of the flange 1.5 inch in any direction.
https://www.supplyhouse.com/Sioux-Chief-889-AOM-3-x-4-Full-Flush-889-Series-Offset-Closet-Flange is the ABS version, and
889-POM is PVC. https://www.homedepot.com/p/Oatey-3...ge-with-Stainless-Steel-Ring-436062/303826505 is out of stock. https://www.homedepot.com/p/JONES-S...or-4-in-Schedule-40-DWV-Pipe-C58434/315676103 can be ordered.

https://www.homedepot.com/p/JONES-S...r-Cast-Iron-or-Plastic-Pipe-C40-320/100168417 has a 1 inch offset, but I suspect it is more likely to interfere with a joist. It is wider I am thinking. If you try it out, you might post some dimensions for the next person who might consider it. The 2 inch part of the description may be how far down it goes, but I don't know where they are measuring to.

Some offset flanges have been notoriously bad. These are good.

What I would like to do is move the toilet over a couple inches to the left, see yellow arrow, it is roughly 3" off the joist now. I do not want to go to the other side of the joist. Since I no longer want to mess with DWV routing, my thought was to cut the stack at the bottom of the PVC coupling and replace with ABS and top it off with a 1.5" offset flange, ABS as well. Though the last response from Jeff has me thinking. Regarding the offset flange quality, it seems anything offering 1.5"+ is going to compromise flow.

how many inches do you want ? cut the 90 off glue another one on use a offset if you have to , worse case head out that joist no biggie

I had thought of this, but assumed there would not be enough meat on the remaining pipe. I measured it last night and with the kerf of a blade I would have right around 1.5" left if I cut at the end of the 90. It would pretty much be hub to hub once glued up, but it would work

 

[Reach4]

Sioux Chief 889-AOMPK - 3x4 FullFlush Offset Flange will pass a 3-inch ball, and your trapway is much smaller than that. So it is not much of a compromise. https://www.siouxchief.com/Products/889-AOMPK
https://www.amazon.com/dp/B01FOFZW7G says 7x7x5, so 5 would be height.

A Reed Socket Saver https://www.amazon.com/PPR300-3-Inch-Plastic-Fitting-Reamer/dp/B005STKRTW could let you get down to the socket of the bend.

A plumber who has done it before will probably be worthwhile.

Get the flange. Be very careful that you have the vertical space before cutting pipe/fittings.
https://media.oatey.com/m/5a851fd79...oset-Flange-With-Metal-Ring_SUBMITTAL_001.pdf see the A - F dimensions (4.47-0.37=4.10 inch), so that would seem to be the easier one to fit in... not a lot of height.

 

[Jeff H Young]

cut it right at the new hub of 90 and glue on a new 90 get rid of the pvc looks better and generally no one likes glueing disimilar plastic even with green glue thatll give you a couple inches

 

[plumb_bum]

cut it right at the new hub of 90 and glue on a new 90 get rid of the pvc looks better and generally no one likes glueing disimilar plastic even with green glue thatll give you a couple inches

Just to confirm you are saying to cut it here, red line at lower hub of the 90.

 

[Jeff H Young]

looks to me approx place to cut thattl move it 1 3/4 inch i belive cut another 1/4 if you have room