Hello,

I am moving a toilet to the other side of the main stack and wanted confirmation on what is the right/best way (to code) to do it. At the old toilet space a tub drain will be placed. Here is a photo of current plumbing.

The stack in 4 inches. On the right there is a santee where the old toilet entered.
On the left is 3 inch drain (that comes from shower and laundry that Wye in the main stack below the old toilet drain.

The question is: Should the santee be replaced by a double tee for new toilet on the other side and on this side be used for the tub drain?

Or is it best to cut out the top elbow going into the Wye and use that entry point for the new toilet drain? This would lead to the cut drain being wye’d into the santee on the right and picking up the new tub drain as well. Thoughts, advice, questions are welcomed. Thanks in advance!

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Edited 3 times.

if i'm understanding you correctly, a double san tee should be fine. put a bushing in the old toilet side and the tub is stack vented thru the top of the double san tee.
if it makes the piping for the tub easier then you can use a side inlet san tee.
these come both left or right side inlet.

Ok. Thank you!

So that is the better option? Would I have any issues with sewage crossing the double santee?

If you planning on putting the double tee on it’s back, Do not

either option will pass my (MA) code.
as with any back to back installation, snaking could be difficult.
personally i would use the side inlet tee,
nomenclature = 3 x 3 x3 x 2 side inlet sanitary tee.
if possible, run full size 2 inch for the tub drain, use a 2 inch P-trap with no plug on the bottom. just put a 2 x 1 1/2 bushing into the inlet of the trap to catch the tub waste outlet.

In my opinion the double sanitary tee would not be to Illinois code. 890.1320(m) says

m) Back-to-Back Fixtures. Back-to-back fixtures shall be installed with fittings that
will prevent mixing of the discharge prior to a change in direction of flow of the
discharge from each fixture, or shall be installed with fittings especially designed
to eliminate throw-over or backflow of the discharge from one fixture to the other
fixture.

I would turn the tee around and tie the tub into the 3" line. You'll need to vent the tub.



Edited 1 times.

kinda technical here..
with a double san tee being used,because of the bushing, the center of the inlet of the tub is higher than the center of the toilet. so technically they are not back to back. since the tub enters higher then it is stack vented over the toilet.
under your definition the side inlet san tee would be prohibited.

Even with a bushing in a double san tee, the centers would be the same. The invert would be higher. Also with a side inlet tee, the fixtures are not back to back so this paragraph would not apply. I agree with the side inlet tee both fixtures would be stack vented.

Quote

.....the centers would be the same. .....

probably, but, not certainly:










yep, i am sometimes called a PITA




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"Measure Twice & Cut Once" - Retired U.A. Local 1 & 638



Edited 1 times.

tom, after i posted i realized the centers would be the same.
i think my code says the tub must enter "higher" than the toilet.
so, how does one calculate what "higher" means ?

California code -
"No fitting having more than one inlet at the same level shall be used unless such fitting is constructed so that the discharge from one inlet cannot readily enter any other inlet. Double sanitary tees shall be permitted to be used where the barrel of the fitting is not less than two pipe sizes larger than the largest inlet, (pipe sizes recognized for this purpose are 2 inches, 21/2 inches, 3 inches, 31/2 inches, 4 inches, 41/2 inches, 5 inches, 6 inches, etc.) (50 mm, 65 mm, 80 mm, 90 mm, 100 mm, 115 mm, 125 mm, 150 mm, etc.)."

Illinois code (seems like a contradiction on double san tee between the 2 sections) -
"i) Changes in Direction. Changes in direction shall be made in drainage piping by the use of 45 degree wyes, long sweeps, short sweeps, quarter, fifth, sixth, eighth, or sixteenth bends, or by a combination of these fittings. Single and double sanitary tees and short sweep quarter bends shall be used in drainage lines only where the direction of flow is from the horizontal to the vertical and may be used for making necessary vertical offsets between the ceiling and floor above. (See Appendix J.Illustrations B, C and D.) Exception: A short sweep drainage quarter bend of less than 3 inches diameter and placed in a horizontal to horizontal position for a stack vent arm may be used to receive graywater.

j)No fittings having a hub in the direction opposite to flow, or tee branch, shall be used as a drainage fitting. No running threads, bands or saddles shall be used in the drainage system. No drainage or vent pipe or fitting shall be drilled or tapped.

I agree that the Illinois code is vague, hard to understand, and/or poorly written. The hub opposite direction of flow applies, I believe, to hub and spigot cast iron. It is completely ignored with respect to dwv pvc although the code does not specify that. If you look at the illustrations cited they do not show a double wye. In 30+ years of plumbing construction, I have never seen anyone install a double wye in the drainage system (OK in the vent). I think it would be a hard sell to get any plumbing inspector to approve it.

Most codes will allow a sanitary cross to be installed for back to back toilets unless they are blow out type. Usually residential toilets are not blow out. Using the 3” drain would lead to improper venting or a much more difficult job to get proper venting

Wouldn't a double fixture fitting be applicable here?