Waste Line Size From Toilet To Septic

[RustyKnuckles]

New construction. One bedroom, one bath home, for my retirement. We are out in the country, and no building codes are in effect, except for septic installation, which we passed.

My cousin is a licensed septic tank installer in my area and I helped him do mine. We used 4" sewer pipe throughout the intake and outflow and laterals, however, when the foundation contrator put in the footing, he put in a 3" piece of drain pipe through the footing. So my cousin used a 4" to 3" adaptor to go through the footing. Now I need to install the rest of the drain line coming from the toilet, bath/shower. Should I use 3" from the toilet to the footing, or use 4" and then use a 4" to 3" reducer to connect it to the 3" line going through the footing? All opinions are welcome. Thanks.

 

[Reach4]

Use 3. You don't want the path from the toilet to reduce on the way. The exception is that you can use a 4x3 closet bend (closet elbow). This outputs to 3 inch fittings and pipe, but uses 4 inch closet flange stuff.

PVC

I would use pressure rated schedule 40 pvc pipe vs foamcore. I am not saying that foamcore is not sufficient, but the price and weight savings of foam core are not that significant.

https://www.menards.com/main/plumbi...490-c-8571.htm?tid=1694497447952337604&ipos=1

In 4 inch pipe, there is schedule 40 and there is thinner stuff with different dimensions. I don't see thinwall 3 inch, but that doesn't mean it does not exist.

 

[Sponsor]

 

[Sylvan]

A Code question was about reduced the waste line going through a concrete floor and the correct answer was " you cannot decrease a waste line"

In this case, you would be much better off using 3" PVC rather than trying to chop the 3" sleeve to make it into 4 "

Schedule 40 of course goes without saying a 3" line can easily handle all the fixture units connected to it

 

[RustyKnuckles]

Thanks. So best bet would be to use a 3" toilet flange and also 3" all the way to the footing pipe?

 

[Reach4]

Thanks. So best bet would be to use a 3" toilet flange and also 3" all the way to the footing pipe?

I would use a 4x3 closet bend (closet elbow) with a 4 inch closet flange. You can get a nice "Code Blue" outside compression cast iron closet flange that does not require gluing. If you glued outside, and later had to rip that up, you could glue in an inside 4 inch. Gluing is not bad, but compression gives you an easy do-over if you like.

This is not to say that a 3 inch closet flange outside of a 3 inch pipe is not good.

 

[Sylvan]

Today most 3.5 GPF toilets have been replaced with the low flow so 3" would be fine as a 4" you would lose the scouring action to prevent slime build up which causes foul smells and stoppages as too big of a line does not allow solids to flow downstream properly (not enough volume)

 

[RustyKnuckles]

I'm using an older toilet that is not a low flow. Most likely it is a 3.5 GPF toilet.
Mama had to have it because it's blue.

 

[Reach4]

I'm using an older toilet that is not a low flow. Most likely it is a 3.5 GPF toilet.

Still 3 inch, because you are going into 3 inch, right? Three inch is OK for more than one toilet. Plenty big.

 

[RustyKnuckles]

OK. For flooring I'd like to use tile over Hardie backer, for a total height of 3/4" above the subfloor, which is plywood. Which Code Blue water closet flange should I get? I've done a lot of carpentry and framing, but have never installed a toilet flange in new construction before.

 

[Reach4]

OK. For flooring I'd like to use tile over Hardie backer, for a total height of 3/4" above the subfloor, which is plywood. Which Code Blue water closet flange should I get? I've done a lot of carpentry and framing, but have never installed a toilet flange in new construction before.

They come in different depths depending how far down the flange has to go to reach the pipe (or spigot on the bend). Since you can cut the pipe/spigot, I think.

Code Blue No Caulk Closet Flange *outside*
C40320 3 pipe x 2 depth ***
C40420* 4 pipe x 2 depth
C40430* 4 pipe x 3 depth
C40440* 4 pipe x 4 depth

 

[RustyKnuckles]

Thanks Reach4, I'll reach for the C40440 probably.
Gotta get into the crawl space and make sure.
But I'm figuring the more length, the more room for error I'll have. Yes?

 

[Reach4]

https://images.homedepot-static.com/catalog/pdfImages/6e/6e4779c2-2a02-4f71-8f61-4f363327cdce.pdf
https://www.jonesstephens.com/product/c40440/

Pictures sure look different. I suspect the HD one is right, oddly enough.
I think you will want the product in hand before you cut the pipe to length.

 

[Jeff H Young]

If you were building to code where the main went from 3 inch to the 4 inch a clean out would be wanted. In anycase concider cleanouts on your build.
I pretty much only have used Copper, cast iron , clay and abs, and cpvc, . with limited amounts of pvc (outside the buillding) on drains and sewer. In ABS I think is all foam core, never heard of pressure in abs . In PVC a lot , or mostly on sewer lines (outside) many use thin wall I think its sdr35 but not legal inside building nor do I recomend , it should be called DWV inside. As for "presure pipe" are you guys using sch 40 water pipe thats normally for water mains?for DWV or something differant?
A 4x3 closet bend is fine and the only exception to reducing sizes. Or going all 3 inch is fine too. I like the 4 inch flange better but cant really support my reason. not a big deal.
Enjoy your new home and retirement> I really like the 1 bed 1 bath plan . visitorswelcome till sundown! Ittl be great to see the inlaws there is al ovely hotel a few miles away ha ha!

 

[Reach4]

As for "presure pipe" are you guys using sch 40 water pipe thats normally for water mains?for DWV or something differant?

Some 4-inch PVC is dual marked.

I like overdoing it, so I would go solid suitable for pressure. I figure it would give margin, in case I did something else a little below standard -- such as preparing the bed under the pipe.

 

[Jeff H Young]

Some 4-inch PVC is dual marked.

I like overdoing it, so I would go solid suitable for pressure. I figure it would give margin, in case I did something else a little below standard -- such as preparing the bed under the pipe.

Didnt know that they dual marked the pipe , My question was partialy based on being legal if not marked DWV its not legal for drain.
Ive never plumbed an entire drainage system in plastic other than ABS and its sch40 foam core which I normaly use for sewer as well much better than thinwall sewer pipe . but not as good as the sch 40 pvc pressure

 

[Reach4]

https://www.menards.com/main/plumbi...67-c-8571.htm?tid=-9065884123580761174&ipos=1 says

• Schedule 40 that is triple marked for well, DWV and pressure applications

I had never heard of pipe being separately marked for well applications.


https://www.homedepot.com/p/4-in-x-10-ft-220-PSI-PVC-Sch-40-DWV-Plain-End-Pipe-531103/100156409 says

• PVC schedule 40 DWV pipe is dual marked and can be used in DWV and pressure applications; gradual sloping fittings are used for DWV applications; sharply angled pressure fittings must be used for pressure; PVC schedule 40 is highly durable, with high tensile and impact strength; it is easy to install and has better sound deadening qualities than PVC schedule 40 foam core and ABS foam core; installation requires primer and solvent cement

 

[RustyKnuckles]

If you were building to code where the main went from 3 inch to the 4 inch a clean out would be wanted. In anycase concider cleanouts on your build.

Yes, we put a clean-out right outside the foundation, and I'll put at least one more inside, on the 3" line.

 

[RustyKnuckles]

I just brought home 30' of 3" Schedule 40 pipe. Thanks people, for the help.