Straight 80' run of 3 inch pipe - 1/8 too little?

[FranZ28]

We are putting in a tiny outside bathroom for guests on our property. Currently we have about 12" drop.

The loo will basically flush straight into the pipe, and run straight into the main line, not a single bend. in fact the drain to the street is exactly lined with our proposed sewer line (will be going straight into the old clean out basically).

So - my question is - will the 3" straight handle a 1/8 slope considering zero turns? we could possibly get it to between 1/8 and 1/4 on a 3" pipe.

This is a tiny household, just me and my wife and a guest -

Otherwise we can repurchase 4" -

Thanks

Food for thought: Would buying a higher GPF loo help the 3" on a 1/8?

 

[DIYorBust]

I can't picture exactly what you are saying, but I don't think I would do it unless you can accomodate a closet bend. You may be able to address this problem with a back outlet toilet.

 

[Sponsor]

 

[WorthFlorida]

A 3" or 4" pipe you are allowed 1/8" slope. 1" every 8 feet, therefore, 10" for the 80 ft run. But as DIY stated, the closet bend can put you down nearly that much to start. If you can build a deck with 2x8's and with a finished floor it puts it 8" higher.

 

[Reach4]

So - my question is - will the 3" straight handle a 1/8 slope considering zero turns? we could possibly get it to between 1/8 and 1/4 on a 3" pipe.

Not in California.

Otherwise we can repurchase 4" -

You can use 1/8 with 4 inch, but it may need approval.

See section 708.1 of https://up.codes/viewer/california/ca-plumbing-code-2016/chapter/7/sanitary-drainage#7

 

[Jadnashua]

It's really hard to backfill the pipe and maintain constant minimum slope. 1/8" is really asking a lot. A 4" pipe would allow that, but still, you don't want any flat spots or bellies in the line, so more slope is better. That shallow depth would also mean the chance driving a vehicle over it could become an issue, too.

 

[Jeff H Young]

3 inch should have 1/4 4 inch 1/8th. In 80 foot 10 inches Run 4 inch its the code. Just lay it best you can the pipe has bows in it and if inspector is a real hard ass it might be tough on you.

 

[FranZ28]

Hi all thanks for the replies -

The platform is already 10 inches above ground (where the loo will sit), and the current pipe is 10-12 inches below ground.. Its running along our property line under the wifes flower bed - so zero chance of any weight issues.

I am also aware of the belly shape pipes can take and will make sure any defects will not affect the slope and run the twists sideway and not up/down.

Im going to check the pipes many times.. this is a simple 6x6 outside bathroom in our back yard.

I know the closets gonna cost me a few - but I might be able to get a 20 inch total drop.. on 75 ft thats hopefully going to land me between 1/8 and 1/4 drop..

I dont mind going 4 inch if it will make that much of a difference?

 

[Jeff H Young]

Its pretty simple. 1 figure out how much fall you have per foot 2 if it comes out to less than 1/4 inch fall run 4 inch Pipe. 3 if you have a MINIMUM 1/4 inch fall use 3 inch. but do whatever

 

[FranZ28]

thanks jeff will do -