3" out to 4" Main

[BobMane]

I am planning a remodel adding a bath to a shop / slab on ground. It has existing 4" right outside the wall. I dug under the slab and all looks good except external 4" is somewhat high where 3" will exit bldg.

If you look at the pic it would come out of bldg on the right where the 4" is higher. Around that corner is an RV dump on grade and to the left is the septic that is not set super low. My estimation is I cant get anymore slope in the 4" so in addition to sawcutting the slab might have to core a hole. Hoping to avoid core hole if possible. So part of my question is what is the highest I can set the 3" coming off the closet flange such that I can possibly avoid core drill?

 

[wwhitney]

You could use a rear outlet toilet to come out above the slab.

If you do come out under the slab, you can save 1/2" of altitude (admittedly not very much) with a Fernco 1056-43EB eccentric rubber coupling (for burial only), or a Spears 429-422FE eccentric 4x3 reducer for solvent weld joints.

Cheers, Wayne

 

[Sponsor]

 

[BobMane]

Rear outlet toilet could be an idea...but the whole setup includes shower and sink as well

 

[Terry]

You really need to work uphill on that.
Water flows downhill and don't lick your fingers before lunch.

 

[Reach4]

If you look at the pic it would come out of bldg on the right where the 4" is higher. Around that corner is an RV dump on grade and to the left is the septic that is not set super low.

That line seems awfully shallow for Montana winters.

 

[BobMane]

You really need to work uphill on that.
Water flows downhill and don't lick your fingers before lunch.

what does that mean

 

[Reach4]

what does that mean

Second sentence is humor, but still good advice. I think the first sentence was saying that if there is an option, usually you start at the downhill side and work your way upstream toward the fixtures.

 

[BobMane]

Second sentence is humor, but still good advice. I think the first sentence was saying that if there is an option, usually you start at the downhill side and work your way upstream toward the fixtures.

I see I don't really understand what that means. Does it mean move the fixtures around inside? I did consider popping out of the bldg with that 3" making a turn and connecting to the 4" on the downside (using the theory that the 3" pipe would have an inch more play in it) But at this point I am probably just going to core drill it because doesn't look like there are many options. I already tried reconfiguring inside the bldg but it doesn't work out.

 

[Mr tee]

A 4 x 3" spigot x hub closet bend and 4" ring takes the least room.

 

[BobMane]

A 4 x 3" spigot x hub closet bend and 4" ring takes the least room.

Do you have a link to that?

 

[Reach4]

Do you have a link to that?

Where do you buy fittings?

https://www.supplyhouse.com/Lasco-D330341-3-x-4-PVC-DWV-90-Street-Closet-Elbow
https://www.homedepot.com/p/Charlot...-x-Hub-Elbow-Fitting-PVC003290600HD/203393625
https://www.pvcfittingsonline.com/3-x-4-dwv-pvc-reducing-closet-bend-p330-342.html

 

[BobMane]

Where do you buy fittings?

https://www.supplyhouse.com/Lasco-D330341-3-x-4-PVC-DWV-90-Street-Closet-Elbow
https://www.homedepot.com/p/Charlot...-x-Hub-Elbow-Fitting-PVC003290600HD/203393625
https://www.pvcfittingsonline.com/3-x-4-dwv-pvc-reducing-closet-bend-p330-342.html

usually at a plumbing supply house but this property is middle of nowhere closest thing is home depot. Is the other piece "and 4" ring " different than what is in my picture?

 

[BobMane]

OK so here is where we are now, a plumber (who has now vanished) laid out this job citing 8'x 18" and "should have max amount of working space" for tub, sink and toilet in corner and/or all along back wall of shop. But he was not the one who would deal with the slab. Now That I have started cutting slab with cut and break saw I made it all the way down the 4" side. I can tell going all the way to the wall slab gets progressively thicker due to it transitioning to 12" is a monster job. So I am asking the question if you look at this image (the purple line with question mark) ...can I only go half way to wall and still set plumbing (using any combination of fixture placements on the inside)

 

[wwhitney]

You picture looks like a 3" hub closet flange with a 3" street quarter bend in it. The suggestion was to use a 4" hub closet flange with a 3x4 hub x spigot reducing closet elbow. That may put the closet bend outlet a little higher than you have, particularly if you make sure that the 4" hub-spigot joint is only 1.75" of overlap (the usual for 4") by cutting down any extra length on the hub and spigot (which for those products may come longer than usual as that can be useful for other configurations).

If your top of slab is level, and the closet bend is controlling the height of all the drainage, and if the elevation difference in your photo is sufficient for the horizontal run required to reach your outside 4" sewer at 1/4" per foot drop, then I don't think you particularly need to raise your closet bend outlet. But if you do, the above is an option.

Cheers, Wayne

 

[wwhitney]

PS the layout in your last picture is not clear to me, this is the corner of the shop, and the wall on the right is exterior, with the 4" sewer running along it, with the lowest point of the sewer near the bottom of the picture? If so, then I have the following comments; if not, please ignore them and post a better labeled picture or floor plan.

You could place your fixtures from top to bottom in the picture as shower, lav, WC. You'd need to trench from the shower trap location down the picture to the WC centerline, maybe removing a 6" wide strip of slab? (Others would have more experience on the width, perhaps 6" is too narrow to work in). You'd also need two trenches perpendicular to the first trench, one at the lav center line to bring the lav drain to the shower drain (possibly keeping the trench higher than typical where it crosses your thickened slab edge, to minimize how much of that you have to remove), and another trench at the WC center line. The WC trench could stop short of hitting the exterior wall on the right if you are going to be core drilling through the thickened slab edge and can line up with the WC trench.

In the above layout, you drainage elevation exiting the slab is going to be determined by the lower of (a) the closet bend outlet elevation and (b) the shower trap outlet elevation, after you add 1/4" per foot fall to each of those to reach the edge of the slab. So you'll have to check which of those controls and whether the result is not too low for your existing 4" sewer.

Cheers, Wayne

 

[BobMane]

Again not sure why he said remove slab to wall when toilet is 12" in...I guess tub might be closer than 12 but also not all the way to wall. In this pic I have rough tub drain location and an alt rough location of 48" center drain shower pan. Of course I could move tub, toilet and sink around if is saves cutting

 

[BobMane]

PS the layout in your last picture is not clear to me, this is the corner of the shop, and the wall on the right is exterior, with the 4" sewer running along it, with the lowest point of the sewer near the bottom of the picture? If so, then I have the following comments;

that is correct

You could place your fixtures from top to bottom in the picture as shower, lav, WC. You'd need to trench from the shower trap location down the picture to the WC centerline, maybe removing a 6" wide strip of slab? (Others would have more experience on the width, perhaps 6" is too narrow to work in). You'd also need two trenches perpendicular to the first trench, one at the lav center line to bring the lav drain to the shower drain (possibly keeping the trench higher than typical where it crosses your thickened slab edge, to minimize how much of that you have to remove), and another trench at the WC center line. The WC trench could stop short of hitting the exterior wall on the right if you are going to be core drilling through the thickened slab edge and can line up with the WC trench.

I will try to get my head around that...having a bit of trouble understanding what that looks like.

In the above layout, you drainage elevation exiting the slab is going to be determined by the lower of (a) the closet bend outlet elevation and (b) the shower trap outlet elevation, after you add 1/4" per foot fall to each of those to reach the edge of the slab

If WC is right next to shower ptrap isnt the elevation almost identical? I had WC placed next to shower to avoid elevation dropping even more from shower ptrap to WC.

 

[wwhitney]

The layout I was attempting to describe earlier. For a tub the trap would be closer to the wall so it might be a bit different.

Cheers, Wayne

 

[BobMane]

You could place your fixtures from top to bottom in the picture as shower, lav, WC. You'd need to trench from the shower trap location down the picture to the WC centerline, maybe removing a 6" wide strip of slab? ..... You'd also need two trenches perpendicular to the first trench, one at the lav center line to bring the lav drain to the shower drain (possibly keeping the trench higher than typical where it crosses your thickened slab edge, to minimize how much of that you have to remove), and another trench at the WC center line. The WC trench could stop short of hitting the exterior wall on the right if you are going to be core drilling through the thickened slab edge and can line up with the WC trench.

I can switch the order like you have it and I can use a shower (or maybe center drain freestanding tub). 6" would be ideal I could do up to about 8" before getting too thick.

 

[wwhitney]

FYI, sizes in the drawing above (per the UPC):

Lav vent through the roof, lav drain in the wall, and downstream should be 2" (* see below *)
Lav trap arm can be 1-1/4" or 1-1/2" to a san-tee in the wall, e.g. a 2x2x1-1/2 san-tee.
A tub can use a 1-1/2" trap and 1-1/2" trap arm, which runs up until it joins the 2" lav drain (wet vent). Then the trap arm is limited to 42".
A shower would need a 2" trap and trap arm, or a tub could use a 2" trap and trap arm. Then the trap arm is limited to 60".
The WC and downstream has to be 3", obviously.

The best practice for joining the WC is with a horizontal wye with the WC coming in the branch inlet, e.g. a 3x2x3 wye created with a 2" bushing in the straight inlet for the 2" lav + shower/tub drain. Then the WC closet bend points at a 45 degree angle to the wall to go straight into the wye branch inlet.

A cleanout or two should be added to the above layout, not sure what's best.

Cheers, Wayne

(*) If this is the only vent on the whole system, then you need a 3" vent, the UPC requires the aggregate vent area through the roof to match the minimum allowable building drain, which would be 3". And then with a 3" vent, you'd need to use a 3" lav drain which would be some trouble; perhaps a different layout would make that easier. But if the existing "RV dump" has a 3" vent up above the roof plane, then that suffices and you only need a 2" vent for your WC.