Second Bathroom DWV Feedback (Isometric Schematic)

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tshannon

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Hello,

I have made use of the professional advice goldmine on this forum many times in the past, but always by reading existing threads. With my latest plumbing project I figured it's time to post a thread of my own! I am firmly in the DIY class, and I would love advice from others out there (DIYers and professionals alike) so that I can learn more about proper plumbing techniques. Oh, and my city uses the 2019 California Plumbing Code (based on 2018 UPC). So, enough introduction, here's the project:

I am hoping to add a second bathroom to my house. The trouble is, my house is on a slab and all the existing DWV piping is under the finished floor or inside finished walls. While not entirely out of the cards, running what amounts to a second sewer lateral is something I would prefer to not have to do to get this bathroom built. Luckily, there is an accessible cleanout for the under-slab piping, and that's where I am hoping to hook up the waste network for my second bathroom. Due to the size of the cleanout (2") and it's elevation, I plan on using a macerating pump from Saniflo in this second bathroom. I know that macerating toilets don't always get a lot of love on this forum, but it seems like the best solution for my situation. I'm definitely open to hearing alternatives though I am also curious to hear feedback on this macerating solution. See the diagram below:

second_bathroom_2021-01-22.png

In case it's hard to read, I've uploaded the full-resolution schematic here.

There are probably other things I'm doing wrong, but the two key areas I've been worried about are:

1. With the macerating toilet discharging upstream of shower/bath 1, I might be putting myself at higher risk for sewage backing up into shower/bath 1. I think nearly any bathroom drainage system theoretically has the potential to back the toilet up into the shower given a large enough clog in just the right spot so I'm not sure if this is unique to my proposed plan or not. Perhaps it's just more likely in my planned layout.

2. With the existing bathroom, plus the laundry room and the proposed second bathroom all discharging into the same 2" branch line, I think I would be beyond the maximum number of fixture units for that 2" line. Here is how I figure it based on California Plumbing Code tables 702.1 and 702.2(2):
Laundry = (3.0 units clothes washer + 2.0 units) = 5.0 units
Existing bathroom = (1.0 units lav + 2.0 units shower/bath)= 3.0 units
Second bathroom = (4.0 units macerating pump @ 27 GPM) = 4.0 units​
...For a grand total of 12.0 units on a 2" line. As far as I can tell, 8.0 units is the max allowed per CPC 703.2
Is my proposed plan dead on arrival, or is there some way to make this work without tearing up the floor of my bonus room, garage, and driveway for another sewer lateral?

Apologies for such a long post, but I figured a bit more detail is better than being vague. Thank you all for your fantastic advice over the years and for helping DIY'ers like me get more educated!!
 

wwhitney

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On the primary question, yes I think you are out of luck, with the 2" line. Although if you could get a macerator that pumps at only 15 gpm, and change your washing machine from a standpipe to draining into the laundry sink, then you'd be at 7 DFUs. Getting a 3" line to the new bathroom location is likely a better choice though, you can route it outside if that would help.

Also, on your existing drawing, the shower venting is not correct, it should come off the shower trap arm before the laundry drain ties in. Not sure if that's a drafting oversight, or an actual non-compliant condition.

Cheers, Wayne
 

Reach4

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Vent for shower/bath 1 needs to be in the trap arm. It is probably ok for real, but not in the drawing.

WC 1 vent is probably not OK in the drawing.
 

tshannon

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Thanks for your replies Reach4 and wwhitney!

Regarding the existing, original-to-the-house piping (in black) I had to sort of infer some of the pipe connection details. I was working off some photos I snapped a while back while some of the drywall was removed for electrical work. So my drawing could be incorrect or the plumbing could actually be out of compliance. Either way, those pipes are basically inaccessible so any issues with those pipes came with the house and are here to stay it would seem :(. I realized it's not clear from the drawing but the existing vertical WC 1 vent is 4" (though I think that doesn't change my proposed plans at all)

Regarding the proposed new piping, I like those ideas to reduce the fixture unit load of the 2" pipe -- it might work.
 

tshannon

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Although if you could get a macerator that pumps at only 15 gpm, and change your washing machine from a standpipe to draining into the laundry sink, then you'd be at 7 DFUs.

I was able to find a macerating toilet that outputs 15 GPM, so that's great. I can also easily seal off the clothes washer standpipe and convert my washer to drain into the laundry sink, putting the total load on the existing 2" pipe at 7 DFU. Thanks for the great idea. The only tradeoff is that the lower-flow pump will not accept shower waste (lav only), so my planned 3/4 bath will have to be downsized to a 1/2 bath. That's a trade I'm fine making.

What about my other concern: That the macerator could potentially pump into shower/bath 1 if there is a clog in that 2" line? Is that a no-go situation or basically just something to be aware of?

Thanks all!
 

James Henry

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You don't have to worry about the 2" line getting clogged because the waste will be practically liquified by the pump inside the tank. I know of a gang bathroom that has 3 toilets on it and is pumped through a 2" line and it never gets clogged.
 

James Henry

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Just a friendly warning. DO NOT put wipes or paper towels anywhere near the bathroom where someone might be tempted to throw them down the toilet. I wouldn't want to be the person who has to unjam the macerating motor.
 

tshannon

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Just a friendly warning. DO NOT put wipes or paper towels anywhere near the bathroom where someone might be tempted to throw them down the toilet. I wouldn't want to be the person who has to unjam the macerating motor.

Haha, yeah we're already planning that bathroom's "do not flush other stuff" sign :D

You don't have to worry about the 2" line getting clogged because the waste will be practically liquified by the pump inside the tank. I know of a gang bathroom that has 3 toilets on it and is pumped through a 2" line and it never gets clogged.

I was thinking more about, say, the shower/bath 1 sending a hairball into the 2" drain line and having that back up the slurry, but also very good to hear about your experience with the triple-toilet setup. Thanks, it gives me a bit more confidence!
 
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