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Small Cabin Forum / Cabin Construction / Rear discharge toilet help
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Nobadays
Member
# Posted: 29 Nov 2020 14:01
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We are looking to install a half bath in our loft, the stairs are steep and narrow so we neither one like to go down them at night when half asleep.

The vent stack exits through the loft at the opposite end from where our bed is. (The loft is about 14' deep and 24' wide) To plumb into the 3" vent stack for a conventional floor discharge toilet would require cutting down through the ceiling of the bathroom below then laterally through the wall into the stack. The reason being the vent for the shower and bathroom sink is plumbed in just below the loft floor... so I would have to drop below that fitting. No bueno!

My best option is to cut a fitting in at the appropriate height (not sure of this height) above the loft floor and extend the pipe to where the Rear Discharge toilet will be placed. I have about 3' of vent stack to work with above the loft floor. This should allow room to put 3 fittings: 3" for toilet, 2 - 3x1 1/2" for sink drain/vent. My understanding is there isn't a need for an additional vent for the toilet... I think this is called a "wet stack" drain.

All this said, guidance with pictures would be appreciated! Would the current shower/sink vent for downstairs need to be rerouted to above the upstairs toilet? Or is this part of the "wet stack" venting. Wet stack venting is allowed here if I read the code correctly.

One of my biggest issues... I am unclear if a rear discharge toilet still uses a standard toilet flange, but mounted on the wall instead?? Pictures please if you can find them, I can't seem to.

Here is the toilet we plan to use... TOILET

Picture of where the stack comes through below.... the toilet will be mounted with the back toward the roof slope, a storage/plumbing box built in behind it.... where the boot rack is.
IMG_5858_resize_16.j.jpg
IMG_5858_resize_16.j.jpg


paulz
Member
# Posted: 29 Nov 2020 20:05
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Can't help you, never even knew they had them. But Ill bump your thread with this:

Went to Ace hardware today for a new toilet seat, hinge broke on the old one. So I'm walking down the main isle thinking they must have a toilet seat or two. Went down the plumbing isle, rounded the corner and holy smokes! A wall of toilet seats! Long, short, open, closed, padded, slow closing.. I finally grabbed one but I've an easier time picking out cars.
20201129_131933_resi.jpg
20201129_131933_resi.jpg


Nobadays
Member
# Posted: 29 Nov 2020 20:12
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Dang... too many choices!

Brettny
Member
# Posted: 30 Nov 2020 07:09
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Did you try each one out bare ass Paul? Lol

You could raise up the toilet on a pedestal and plumb like normal because all the new plumbing would be above the current floor level. Either way you choose to do it I would get the toilet prior to doing anything. Your playing with inches here and dont want to mess something up.

Theres also a way to do all the plumbing from the top but you would need to make a bigger hole in the floor than for just a toilet flange.

Nobadays
Member
# Posted: 30 Nov 2020 08:43
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Brettny... yep, we figured we should get the toilet first so we could position it, slide it around until in the right place. A pedestal is pretty much out as we are already under the slope of the roof. Hoping to position the toilet as far back as possible but forward enough that when you sit/stand you don't have to duck to not hit your head.

Realized I have an additional issue. The vent pipe for the water heater also comes up through that box in the picture.... toward the front. We plan to build a wall directly out where that box is now - to enclose the soil stack and gas vent.... and we plan to put a very small sink along that wall, so that wall would enclose the sink drain pipe and vent pipe. Except, I have to figure out how to go around the gas vent stack to reach the soil stack behind it. I'm thinking double wall studs out from the cabin wall/ceiling just far enough to allow the bends needed to get around the gas vent and back into the stud wall. The vent doesn't matter but I don't want to cause issues with the sink drain by having multiple bends in it.... maybe no way to avoid it though. May just need to make a clean out for that drain accessible.

This is meant to be a tiny bathroom so I need to keep things as tight as possible yet not cause future problems. I'll try to sketch things out and post that to see if anyone sees another way... and/ or if my plumbing plan looks good.

Brettny
Member
# Posted: 30 Nov 2020 10:51
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With what is in the way and the fact that you will need to rework things it may be time to just bite the bullet and open up part of that floor. This way you can re work things easily and then cover the floor back up. Personally I wouldnt want a wood floor in a bathroom anyway.

Nobadays
Member
# Posted: 30 Nov 2020 11:08
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Except... it won't do any good to open the floor. Directly beneath the floor is a 3x1 1/2" fitting that the vent for the shower and bathroom sink plumb into the soil vent stack. I would have to cut in below this fitting to put the 3x3 for the upstairs toilet.... in order to do that I would have to cut through the downstairs bathroom ceiling then through the wall into the vent stack. It could be covered up but why when they make a rear discharge toilet...

I did do some reading on the manufacturer's website and I see that you don't need a standard toilet flange on the wall. The p-trap adapter from the toilet can be cut to length then glued into a 3" abs fitting. The p-trap adapter has a gasket in a bell that the toilet is then pushed into before screwing it to the floor. One question answered!

The sink drain is the issue... getting around the gas vent stack. I'm thinking 3 45* s... 45 out another 45 to make a 90 then 45 back into the soil vent stack fitting... also angled to 45 off center. That will be hard to visualize! Thinking I could use a mechanical vent for the sink and eliminate the extra vent pipe. They are allowed here by code... our kitchen sink uses one.

I'll try to draw something up.

Nobadays
Member
# Posted: 30 Nov 2020 17:30
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Here is a sketch of what I want to do.
UpBathDesignpage0.jpg
UpBathDesignpage0.jpg


Brettny
Member
# Posted: 1 Dec 2020 06:15
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3 45* fittings horizontal like that could cause issues. Not sure how to get around that though.

Nobadays
Member
# Posted: 1 Dec 2020 08:57
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Brettny... yeah I know, don't like it. Thinking of putting an access to the right of the sink and a clean out plug at the end of that run.

Venting is my biggest question now. I have the 1 1/2" vent for the downstairs sink and shower coming into the stack just below where I plan to plumb the upstairs toilet in. I'm thinking that won't work. I believe I need to cap that off and bring that vent up above the new sink drain fitting upstairs.... or put a mechanical vent on that as well, under the floor. It is accessible from the water heater closet below. Barely...

The big one.... and I hope I'm wrong.... is I think I have to bring a 2" vent from just above where the downstairs toilet plumbs in, up and above the sink drain upstairs. I HOPE NOT.... does anyone know? And can that have a mechanical vent as well... might simplify it a little. OR... is the present vent stack enough...WITH an upstairs toilet plumbed into it too??

I've looked at a lot of venting diagrams but they all seem different. Can't find a YouTube video addressing rough in plumbing for upstairs bathroom addition. People do this all the time so there is a way! If I need a separate vent on the downstairs toilet, this project just got a lot tougher!

paulz
Member
# Posted: 1 Dec 2020 09:29
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Trying to follow along.. What's the wide section preventing the sink drain from going behind the vent pipe?

Nobadays
Member
# Posted: 1 Dec 2020 10:38
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Paul... the pipe in front of the soil vent stack is a gas vent for the water heater. Can't move it so gotta go around it.

I think I've answered my question about downstairs toilet venting. Yes... it will need a vent between the toilet flange and the 3" vent stack.... that vent to be brought all the way up above the drain for the upstairs sink... dang! Or a new 3" drain for the upstairs toilet.

I found this on another forum with someone asking the same question after the inspector called him out.... the guy answering cited the sections of code so I think it is legit.

"To be code correct one of two things needs to happen.

1. The uptairs toilet could be connected to a separate stack as was described by the inspector or:

2. A vent needs to be installed between the downstairs toilet and the stack.

The theory here is, A direct line from the toilet to the stack is classified as an "unvented fixture arm" and an unvented fixture arm may not be attached to a stack if there is a toilet above the point of connection on the stack. By placing a vent on the lower toilet fixture arm the portion of pipe from the lower toilet to the vent is now the fixture arm while the remaining section of pipe from the vent to the stack is a "Vented branch" which may be attached below a toilet."

Now I need to crawl under the cabin and see what I have to work with.... I don't think there is enough room between the toilet flange and the stack for a fitting. To run a second 3" drain might be tough.... I could vent it with a 2" into the existing soil stack I think, but, just not sure there is enough room between the wall and the existing stack to pass a pipe behind it.

Maybe... need to measure. A new drain would probably be the easiest way, I could bump the wall out a few inches and avoid those 45's around the gas vent as well. A new drain could come down behind the water heater in the back corner though. Now to figure out how I could tie that into the drain under the cabin. (Obviously thinking out loud here )

Thanks for bouncing this around with me!
IMG_5859_resize_87.j.jpg
IMG_5859_resize_87.j.jpg


Nobadays
Member
# Posted: 1 Dec 2020 19:40
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Looking more and more like my "easy" upstairs bathroom project is way more complicated than I first thought. It is still on the list but is now bumped to spring... probably.

Crawled under the cabin and the plumbing was different than I expected. The main 3" drain line basically starts at the downstairs toilet flange/closet bend and runs in a straight line from there to where it disappears underground near the perimeter. The 3" soil vent stack is plumbed into this main drain 2/3 toward the top of the pipe maybe about 2-3' down stream from the closet bend. It travels back toward and behind the closet bend where it turns up and goes through the floor.... straight up and through the roof.

My thought of bringing a separate waste line down from upstairs probably wont work as I'd have to thread the new line between the closet bend and the soil stack... not sure it would be possible... might be. All the plumbing under the cabin is wrapped in 3.5" fiberglass insulation, including the wast lines, so it's really hard to see what I actually have. But, I did some measuring and a new 3" waste line might drop down between the current line to the toilet and the adjacent floor joist... would be tight.... except there is an electrical wire running right through that space... arghh!

The good news, and I'll confirm it once I do pull all the insulation off the pipes, is I think there is room between the closet bend and where the 3" soil vent is plumbed in to insert a 3x3x2 fitting allowing me to run a separate 2" vent for the downstairs toilet, which I'll also plumb the vent for the shower/sink into.... maybe much easier to thread that through the obstructions up through the water heater closet, through the upstairs floor and up above where I can plumb in the upstairs toilet fitting. I am pretty sure that would meet code and more importantly properly vent the downstairs toilet. This then allows me to dump the upstairs toilet into that vent stack... which will be the vent for that toilet.

It did become apparent today that none of this can happen until I move the water heater out... so as long as we are using our main water system (not the winter tanks in the loft) the water heater is in use as well. Just not sure I want to pull insulation away from pipes until winter is over, or the system is drained.

We'll see..... more to come down the road!

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