# 3" or 4" ?



## KillerToiletSpider (May 27, 2007)

Williams Ex Co said:


> I'm not a pro plumber but I have done lots of excavations for septics and sewers.... My take on this is that the 3'' pipe works better in-as-much as the smaller diameter pipe doesnt allow the liquid and solids to separate as much/quickly... Dunno if thats right but it sounds plausible. Thats my story, I'm stickin' to it....


If you are having separation issues it is a pitch problem, not a size problem.


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## The Coastal Craftsman (Jun 29, 2009)

KillerToiletSpider said:


> If you are having separation issues it is a pitch problem, not a size problem.


 
Thats a common problem. To much fall will leave the big boys behind.


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## Ron The Plumber (Oct 10, 2006)

BCConstruction said:


> Thats a common problem. To much fall will leave the big boys behind.



Not true.


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## Williams Ex Co (Dec 25, 2007)

KillerToiletSpider said:


> If you are having separation issues it is a pitch problem, not a size problem.


 

What is the proper amount of fall? I have always tried to aim for 1/4'' per lineal foot. Is that too much? Thanks...


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## Ron The Plumber (Oct 10, 2006)

Williams Ex Co said:


> What is the proper amount of fall? I have always tried to aim for 1/4'' per lineal foot. Is that too much? Thanks...


Outside foundation 1/8" is min, 1/4" is idea and 1/2" or more works just as it's suppose to.


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## KillerToiletSpider (May 27, 2007)

Williams Ex Co said:


> What is the proper amount of fall? I have always tried to aim for 1/4'' per lineal foot. Is that too much? Thanks...


With the advent of 1.3 GPF toilets we slowly came to realize that 1/4" per foot was actually too much, and that 1/8" caused far less problems, but you should be installing it to your states code.


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## Double-A (Jul 3, 2006)

The smaller 3" pipe will allow solids to carry further downstream than a 4" pipe will. This has to do with how much flooding occurs in the pipe during flush and when this flooding becomes too shallow to push solids along any more.

Sanitary sewer systems are designed to run at 60 percent capacity, allowing the other 40 percent for air. Contrast this to storm sewer systems which are designed to run at 100 percent capacity. 

The reason for 3" is two fold. Its cheaper/lighter/easier to install (or so the theory goes) and toilets use less and less water and don't need the bigger pipe to achieve the target of approximately 35 feet of wash down at 1/4" per foot of pitch.

Now that we have all been bored to tears, can we please play nicely now?


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## protechplumbing (Oct 10, 2008)

Sorry for the delay on this one. I missed the e-mail 

Ok, the reason that 3" is the better choice is because of velocity and flow channel depth as Double-A said. You want more velocity to push those turds down the line. Don't believe me?

OK here's is an experiment for you. Get a piece of 2" pipe and a piece of 4" pipe. Set them both at the same pitch say 1/4" per ft. Now crack a sillcock open and put the end of the hose over the top of one of the pipes and set a small object in the line. Time the object to get to the end of the pipe. Repeat with the other pipe(don't mess with the flow rate coming out of the hose during the experiment). Try it with different objects. You'll notice that the smaller line always wins.

The main reason that older houses had 4" water closet lines and you see mostly 3" now'a days is because toilets used to flush 3-4 times more water than they do now. Less water means a smaller pipe. I could get all technical with manning’s equation but I think this dumbed down version pretty much gets the point across.

Got it?


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## spdtrx (Sep 10, 2009)

PPPP Sorry I had to let that one go.:w00t:


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## The Coastal Craftsman (Jun 29, 2009)

Ron The Plumber said:


> Not true.


 
Yes true. I my self have been to many new builds where the fall was far to much for the length of run. What happens is the solids move a lot slower than the water flows so the solids get left behind. Every plumber should know this. Happens a lot in UK with 4" soil and dual flush toilets. Happens less with the 3" as the volume of water to free air space is higher. But i like i have said i see far more blocked toilets over here compaired to UK.


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## Ron The Plumber (Oct 10, 2006)

We have thousands of homes built on hills around here and the sewer lines all go down hill full bubble on the level, there are not alot of sewer stoppages on those lines, so yes I repeat it is not true about too much slope. Don't believe I live around hills, Google Eugene Oregon and see my surroundings.


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## The Coastal Craftsman (Jun 29, 2009)

Ron The Plumber said:


> We have thousands of homes built on hills around here and the sewer lines all go down hill full bubble on the level, there are not alot of sewer stoppages on those lines, so yes I repeat it is not true about too much slope. Don't believe I live around hills, Google Eugene Oregon and see my surroundings.


 
I also have seen sewers with drops which have fully broken a bubble and they have kept clear also. Mainly just because of the volume of water passing through them. With toilets its a different matter. If the toilet is used often it may not cause an issue but if it's used as little as once a day that solid if left behind will almost weld it's self to the soil pipe as it dries out. Flush another one a day later and that will do the same and so on until they build up to a complette blockage. Im just glad i was never the the person to clean them out.


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## Ron The Plumber (Oct 10, 2006)

If there is problem in a line it is because of roots of others problems, slope is not a factor, now not enough slope yes, but more then needed slope/grade is always a good thing,


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## protechplumbing (Oct 10, 2008)

The reason toilets back up less in the UK is due to the toilet design not the drains. You did know that right? 



BCConstruction said:


> Yes true. I my self have been to many new builds where the fall was far to much for the length of run. What happens is the solids move a lot slower than the water flows so the solids get left behind. Every plumber should know this. Happens a lot in UK with 4" soil and dual flush toilets. Happens less with the 3" as the volume of water to free air space is higher. But i like i have said i see far more blocked toilets over here compaired to UK.


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## The Coastal Craftsman (Jun 29, 2009)

protechplumbing said:


> The reason toilets back up less in the UK is due to the toilet design not the drains. You did know that right?


 
Yep thats what i posted them pics for in the other post. The UK pans have a wider throat, outlet and the traps are also a lot more free flowing. They require a lot less back pressure to shift anything in the pan. The traps newer ones that come with the dual flush valves would sometimes give you problems but not very often. The lowest flush setting was never designed to shift solids but most of the time it can. The US toilets are getting better though. I fitted one for my bro in law the other week and the thing would use about 1.5 liters from my calculation and it would take away what ever what put down the thing. Was pretty impressed.


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## protechplumbing (Oct 10, 2008)

try again :no:


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## The Coastal Craftsman (Jun 29, 2009)

protechplumbing said:


> try again :no:


I would also say that the 9 liter flush helps but i have seen that size of here as much as the UK.

Also not every house has a high level cistern like you guys see on TV all the time on english shows. 99% are either low level or close coupled.


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## protechplumbing (Oct 10, 2008)

The correct answer was.......

Toilets are siphon jetted in the USA and they are of a washdown design in the UK.

Do I need to outline the differences between the two and the pros and cons of the two designs?


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## The Coastal Craftsman (Jun 29, 2009)

protechplumbing said:


> The correct answer was.......
> 
> Toilets are siphon jetted in the USA and they are of a washdown design in the UK.
> 
> Do I need to outline the differences between the two and the pros and cons of the two designs?


 
That explains why the pan traps over here gets sucked dry. Upto yet i have only come across that one the other week that really worked as i expected it to. Does this also have something to do with the rubber hose on the fill valve that drains straight into the over flow? Thats another thing the valves in the UK dont have. perhaps you can expalin what that things for. No ones been able to tell me upto yet. :thumbsup:

I thought it might have been for filling the trap back up as they sure do let a lot of water out of the over flow!


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## Ron The Plumber (Oct 10, 2006)

BCConstruction said:


> Does this also have something to do with the rubber hose on the fill valve that drains straight into the over flow? Thats another thing the valves in the UK dont have. perhaps you can expalin what that things for. No ones been able to tell me upto yet. :thumbsup:
> 
> I thought it might have been for filling the trap back up as they sure do let a lot of water out of the over flow!


Correct it helps the bowl water to reach it's operating level after each flush.


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