Back to Back Toilets: Double Fixture vs Double Wye

[SoConfused]

It's a consequence of two requirements: First, that every fixture be vented before (dry vent) or as (wet vent) its fixture drain joins another drain. And second, that horizontal wet venting is restricted to bathroom fixtures.

So in the drawing just above, the right hand WC gets its dry vent connection before the second WC comes in. And the second WC is wet vented by the first WC. As the 2" line is carrying non-bathroom fixtures, if it joined the first WC after its vent but before the 2nd WC, that would make the 2nd WC's wet vent non-compliant. And if the 2" line joined the first WC before its dry vent comes off, that would violate the "vent before joining other drains" rule.

Now if you were to separate the upstream 2" line into two separate parallel drains, one with bathroom fixtures only, and one with the kitchen/laundry, then only the kitchen/laundry would have to join the 3" line downstream of the WCs. And the line with the bathroom fixtures could be used to wet vent the WCs. But I imagine doing that is more trouble that it's worth.

Cheers, Wayne

Gotcha. Thanks!

 

[Jeff H Young]

I sure don't like the heel outlet on its back or the 2 2inch santees. Evidently so confused been going after correcting things good option is post 32 sketch. hopefully based on UPC for all that 2 inch work ( wash machine etc. on 2 inch piping) but if it works good you might not need to rework it not part of scope of work

 

[Sponsor]

 

[SoConfused]

Maybe something like this.
The last toilet drops into a combo fitting with a cleanout on the end.
The far plumbing comes in after the toilets, a 3x2 wye.
The 3" vent for the toilets.

View attachment 75968

This way the toilet waste drops down and out toward the septic smoothly.

Hi Terry and Wayne if you see this - I'm finally ready to get started replumbing these toilets. I had been looking at the fixtures connecting both WCs and the Vent to the main drain as combos and purchased the parts that way. But I see now that the WC on the left is a wye instead of a combo. Why this difference? Would a combo work?

 

[wwhitney]

The left WC is not directly over the 3" branch drain but is close to it, correct? Then any of these three options could work:

(a) flange -- closet bend pointed at branch drain -- horizontal combo
(b) flange -- 45 degree elbow pointed at branch -- combo rolled up 45 degrees
(c) flange - closet bend pointed at a 45 angle to the branch -- wye

(c) is the most compact, I think, in terms of the minimum distance (in plan) from the WC to the 3" branch drain. (b) is also pretty compact (might beat (a), not sure). (a) will require a bit more space between the WC and the 3" branch drain.

So the combo will probably work for you unless space is really tight.

Cheers, Wayne

 

[SoConfused]

The left WC is not directly over the 3" branch drain but is close to it, correct? Then any of these three options could work:

(a) flange -- closet bend pointed at branch drain -- horizontal combo
(b) flange -- 45 degree elbow pointed at branch -- combo rolled up 45 degrees
(c) flange - closet bend pointed at a 45 angle to the branch -- wye

(c) is the most compact, I think, in terms of the minimum distance (in plan) from the WC to the 3" branch drain. (b) is also pretty compact (might beat (a), not sure). (a) will require a bit more space between the WC and the 3" branch drain.

So the combo will probably work for you unless space is really tight.

Cheers, Wayne

Thanks for getting back to me Wayne! I have about 11 inches of vertical space and 8 inches of horizontal space. I think what I was planning matches up to your (b) option. In my terminology I was going to add a 45 degree angle to the pipe coming down from the WC (If I understand correctly that's the "flange" in your options)
Then rotate the combo "down"* to meet the 45. I think I will have room to do this and if I am a little short, I can add a short stub of pipe between the 34 and the combo. I got concerned when I looked back at the drawing from the forum and saw that the fitting there was actually a Wye.

*(When I say rotate the combo "down" I picture it starting with the curved arm vertical.)

I'm curious about your #1. When you say "horizontal combo" are you saying the combo would be laying on it's side parallel with the ground?

 

[wwhitney]

Thanks for getting back to me Wayne! I have about 11 inches of vertical space and 8 inches of horizontal space.

If those are centerline measurements (11" vertically from center line of 3" branch to finish floor above, and 8" from centerline of 3" branch to center line of closet flange, when measured perpendicular to the branch and projected onto a level plane), then that's tight. I think if you use a 3" combo rolled 45 degrees off plumb (or above horizontal) you would need to use a street 45 on the end.

If it doesn't fit, get a 3" wye and a quarter bend or closet bend and go with my option (c).

I'm curious about your #1. When you say "horizontal combo" are you saying the combo would be laying on it's side parallel with the ground?

That's right, except each of the 3 openings would be at 2% slope rather than level. That's the conventional way to do horizontal wet venting.

Cheers, Wayne

 

[SoConfused]

If those are centerline measurements (11" vertically from center line of 3" branch to finish floor above, and 8" from centerline of 3" branch to center line of closet flange, when measured perpendicular to the branch and projected onto a level plane), then that's tight. I think if you use a 3" combo rolled 45 degrees off plumb (or above horizontal) you would need to use a street 45 on the end.

If it doesn't fit, get a 3" wye and a quarter bend or closet bend and go with my option (c).


That's right, except each of the 3 openings would be at 2% slope rather than level. That's the conventional way to do horizontal wet venting.

Cheers, Wayne

Now that you ask that... I just looked back at my measuring picture and I think I cut myself a little short horizontally by the way I measured. It looks like I didn't have the square all the way down the pipe to the bottom of the actual flange. Since that pipe is at an angle I think that may buy me a little space. It's hard to explain so I'll attach the pic here. The 11 vertical measurement is actually from the bottom of the floor joist to the top of the branch. So I have some additional vertical space but I have to use a little of it to convert the flange from 4 inch to 3 inch.

 

[SoConfused]

Sorry Wayne but I just looked at the pic again and the measurement is pretty close to right. It looks like the flange is farther down the pipe in the pic but I have the square against the joist where the flange comes down. So it would only vary by an inch horizontally at most.

 

[SoConfused]

If those are centerline measurements (11" vertically from center line of 3" branch to finish floor above, and 8" from centerline of 3" branch to center line of closet flange, when measured perpendicular to the branch and projected onto a level plane), then that's tight. I think if you use a 3" combo rolled 45 degrees off plumb (or above horizontal) you would need to use a street 45 on the end.

If it doesn't fit, get a 3" wye and a quarter bend or closet bend and go with my option (c).


That's right, except each of the 3 openings would be at 2% slope rather than level. That's the conventional way to do horizontal wet venting.

Cheers, Wayne

Hi Wayne - I'm planning on cutting pipe this afternoon but have one question I've avoided asking because I know you won't like it. I can't do all of this right now. So if I do the toilets as you've shown in post #32 but leave the toilets configuration connected to the 2 inch line upstream, will the venting still work until I can go back later and put the cleanout upstream of the toilets and separate the 2 inch line to join the 3 inch downstream of the toilets? See my drawing,

 

[wwhitney]

I'm confused about the construction sequence. Based on the geometry, the above configuration drawn as planer wouldn't fit.

You could use the upper branch geometry from post 32, with the upstream WC horizontal elbow replaced with a wye for a future cleanout, and then temporarily install it lower down, with the 2" line coming into the future cleanout. Then in the future you'd have to cut the 3 risers and the 3" line before and after the WCs, raise it all up, put in the cleanout, extend the 2" wye underneath, and join everything up with downstream-most wye.

But that seems like a lot of trouble. If I have a chance I'll think about construction sequencing, how to get from the second picture in post 1 to the diagram in post 32 in smaller steps, with at least one WC working after each step.

Cheers, Wayne

 

[SoConfused]

Thank you for answering! My drawing is just a rough draft without accounting for offsets but based on semi dry-fitting it should all fit. It will take me a bit to think through the details of what you're suggesting but while you're here let me just see if I have the basics. What I understand you to be saying is that waiting to move the 2 inch line won't keep things from functioning correctly but there is a better way to do it that will make moving the 2 inch smoother later. Is that correct??

 

[wwhitney]

I'm saying that the connectivity drawn in your first post today isn't a code approved final configuration, but as a practical matter I would expect it to function in the short run. Certainly if you flush a toilet while the kitchen sink, DW, and washer are not in use, it should be any different from the final configuration.

As to make the moving the 2" smoother later, let me think about the construction sequence.

Cheers, Wayne

 

[SoConfused]

Sounds good. Thank you so much Wayne! I check in later before I start cutting. Just so we're on the same page... the 2 inch line will be swinging to the side and not below the 3 inch because I don't have enough vertical space to stack them.
Thanks again!

 

[wwhitney]

Just so we're on the same page... the 2 inch line will be swinging to the side and not below the 3 inch because I don't have enough vertical space to stack them.

Well, that would certainly affect the construction sequence. So you're back to Terry's original layout? That's fine and is probably simpler. [I'm surprised there's not enough room for vertically stacking the two horizontal lines, as they could be 5-7/8" center to center using a 3" wye and street 45.]

Let me think some more about the construction sequence.

Cheers, Wayne

 

[wwhitney]

Looking at this again, and given that you're happy to swing the 2" line out away and then back in downstream, you might consider an earlier idea of Reach4's and going with a simpler change as crudely shown in the picture below. It consists of two adjustments, which could be done in either order:

1) The red line is supposed to show a 2" line jogging out to the side of the lower 3" line (I think I don't have the perspective quite right). So remove the pipe in the cut area, cap the inlet to the low heel 90, use two 45s to jog, then cut in a 3x3x2 wye downstream, with a 2" 45 to complete the jog back and reconnection. Putting the 3x3x2 wye pretty far downstream will be most flexible for any future changes with the WC.

Note that the length of the 2" path is now a little longer than previously, so the required fall is a little greater than previously. So if everything is pitched at exactly 1/4" per foot, doing this would put you a hair under 1/4" per foot. Hopefully somewhere things are pitched slightly more than 1/4" per foot, so you can gain 1/4" or 1/2" in altitude. If this is challenging, then jogging the 2" line the minimum amount necessary to reconnect it with the 3x3x2 wye plus a street 2" 45 would minimize the length increase.

2) On the WCs, remove the 3" pipe section shown and cap the inlet to the double san-tee. Then the green line is supposed to show cutting in an upright combo (or a wye plus street 45 might give you a little more flexibility) and using a quarter bend (possible street) to connect the WC fixture drain to that combo. The challenges are whether there's enough height for both those fittings and whether the angle alignment will work out, as the upper horizontal WC fixture drain is not directly over the lower drain. I think the combo would be shorter, so better for the first issue, but the wye plus street 45 would give you another joint to adjust, so better for the second issue. Worst case you'd have to redo more of the WC fixture drain on the left to get everything to line up.

The result of those two changes is still an acceptable wet vent of the left hand WC by the right hand dry vented WC. WCs don't have any restriction on the vertical location of the vent connection, so it's OK for the left hand WC to drop again before venting. The resulting geometry isn't the neatest, but it should work.

Then if everything is working OK, you can do the following (not drawn)

3) Cut out the capped double san-tee and capped low heel inlet quarter bend, and replace them with a (possibly street) san-tee and a long turn 90, respectively. [Need to verify there is sufficient height.] That cleans up the installation a bit, and changes the vertical to horizontal transition to the required long turn 90 fitting.

And finally, if for some reason the double WC DWV layout doesn't work (functionally or geometrically), as long as the 3x3x2 wye you install in step (1) is sufficiently downstream, you have the option of removing everything upstream of its 3" straight inlet and redoing the DWV, e.g. per Terry's layout.

Cheers, Wayne

 

[SoConfused]

Looking at this again, and given that you're happy to swing the 2" line out away and then back in downstream, you might consider an earlier idea of Reach4's and going with a simpler change as crudely shown in the picture below. It consists of two adjustments, which could be done in either order:

1) The red line is supposed to show a 2" line jogging out to the side of the lower 3" line (I think I don't have the perspective quite right). So remove the pipe in the cut area, cap the inlet to the low heel 90, use two 45s to jog, then cut in a 3x3x2 wye downstream, with a 2" 45 to complete the jog back and reconnection. Putting the 3x3x2 wye pretty far downstream will be most flexible for any future changes with the WC.

Note that the length of the 2" path is now a little longer than previously, so the required fall is a little greater than previously. So if everything is pitched at exactly 1/4" per foot, doing this would put you a hair under 1/4" per foot. Hopefully somewhere things are pitched slightly more than 1/4" per foot, so you can gain 1/4" or 1/2" in altitude. If this is challenging, then jogging the 2" line the minimum amount necessary to reconnect it with the 3x3x2 wye plus a street 2" 45 would minimize the length increase.

2) On the WCs, remove the 3" pipe section shown and cap the inlet to the double san-tee. Then the green line is supposed to show cutting in an upright combo (or a wye plus street 45 might give you a little more flexibility) and using a quarter bend (possible street) to connect the WC fixture drain to that combo. The challenges are whether there's enough height for both those fittings and whether the angle alignment will work out, as the upper horizontal WC fixture drain is not directly over the lower drain. I think the combo would be shorter, so better for the first issue, but the wye plus street 45 would give you another joint to adjust, so better for the second issue. Worst case you'd have to redo more of the WC fixture drain on the left to get everything to line up.

The result of those two changes is still an acceptable wet vent of the left hand WC by the right hand dry vented WC. WCs don't have any restriction on the vertical location of the vent connection, so it's OK for the left hand WC to drop again before venting. The resulting geometry isn't the neatest, but it should work.

Then if everything is working OK, you can do the following (not drawn)

3) Cut out the capped double san-tee and capped low heel inlet quarter bend, and replace them with a (possibly street) san-tee and a long turn 90, respectively. [Need to verify there is sufficient height.] That cleans up the installation a bit, and changes the vertical to horizontal transition to the required long turn 90 fitting.

And finally, if for some reason the double WC DWV layout doesn't work (functionally or geometrically), as long as the 3x3x2 wye you install in step (1) is sufficiently downstream, you have the option of removing everything upstream of its 3" straight inlet and redoing the DWV, e.g. per Terry's layout.

Cheers, Wayne




View attachment 76843

This is extremely helpful Wayne! This sequencing allows me to take steps to correct my immediate problem without causing more work when move forward to get rid of the whole double SanTee and low heel inlet.
This is a very workable solution! You are a gentleman and a scholar!
Thank you for taking the time to type all of that out. May God bless you for your kindness!

 

[wwhitney]

No problem, it's an interesting question and I hope my ideas work out for you.

One thing to be aware of is that step (1) may start allowing some solid waste to accumulate in the dead end low heel inlet of the quarter bend, and step (2) may do the same for the capped inlet on the san-tee. So I suggest using solvent weld caps, and when you get to step (3), be prepared for the possible accumulation. Flushing the toilet several times in a row before cutting the pipes might help. Cutting the pipes a little beyond the fittings if possible may allow you to remove the fittings without spilling anything.

Cheers, Wayne

 

[SoConfused]

No problem, it's an interesting question and I hope my ideas work out for you.

One thing to be aware of is that step (1) may start allowing some solid waste to accumulate in the dead end low heel inlet of the quarter bend, and step (2) may do the same for the capped inlet on the san-tee. So I suggest using solvent weld caps, and when you get to step (3), be prepared for the possible accumulation. Flushing the toilet several times in a row before cutting the pipes might help. Cutting the pipes a little beyond the fittings if possible may allow you to remove the fittings without spilling anything.

Cheers, Wayne

I appreciate the tips on the waste build up. I had to go a little out of order because I it turned out I didn't have everything I needed for step 1 and this was the only time I could get to it this weekend so I did step 2 first. I didn't see anything that would prevent me from swinging the two inch line out as my next step. The pipe down from the WC was 4 inch so I put a 4 x 3 reducer, followed by a street 45, and a short length of 3 inch pipe then the combo. As my last step I did a slip coupling to attach the downstream end of the combo to the drain line.

I've flushed the right hand WC several times and have had no water loss in the left one. Woo hoo!! Swinging the 2 inch line should be a breeze after that. I'm today's work would have been simple for a plumber but it was a 4 hour job for me. I'm still proud!

 

[wwhitney]

Glad you were able to get things taken apart and put back together in the time you had available. I'm not a full time plumber either so it probably would have taken me just as long. But there is one issue with today's work that you'll need to fix:

The pipe down from the WC was 4 inch so I put a 4 x 3 reducer

So unfortunately, that's not allowed, to reduce the diameter of a drain in the direction of flow. The one exception is a 3" x 4" reducing closet bend, and zooming in on your 2nd photo in the OP, I see that is what you had. I don't think any of us noticed the hidden 4" vertical WC drains, as everything below the joists is 3".

As I understand it, your current configuration for the left-hand WC is the following: 4" closet flange above the floor - 4" vertical pipe - 3" x 4" reducer - 3" street 45 - short 3" pipe - 3" combo to connect to the lower 3" horizontal drain (which combo must be rolled about 45 degrees to line up with the street 45). If that's correct, then the simplest option is likely to pull the WC, cut off everything above the 3" combo (hopefully you have and can leave at least 2" of pipe stub to connect to), and then rebuild back up in 3" to a 3" closet flange. If you cut in the 3" combo with (2) Fernco 3005-33 shielded rubber couplings or the equivalent, then you have the ability to rotate your 3" combo if required when rebuilding to the closet flange.

So if the above description is accurate, that's your new step 2.5. Otherwise, please post a photo of how you used the reducer.

Cheers, Wayne

 

[SoConfused]

Good morning Wayne,
What you described is correct. I'm attaching a picture taken during dry fitting. The short 3 inch pipe is too short in this pic as I was just using it to line up my pipes. You can see the reducer just above the bottom of the floor joists. The drop from the toilet flange to the reducer is only about 8 inches. I know there are good reasons for plumbing codes but I just can't see how in this instance, it would be a problem since the reducer goes directly into the street 45, which doesn't seem a whole lot different than a 4 x 3 closet bend set up. Am I missing something?