[Greenbuilding] 2" drain line for a 0.8gpf toilet?

[Joe Killian]

Yes, a well known/documented relationship.
...Well, that inverse relationship can't be extended indefinitely (else 
let's go to 1/2" pipe!).

   When the diameter gets smaller than the solids being transported it 
stops up (barring sufficient pressure to transform & move the solids).  
So the question is how far can we extend that inverse relationship 
before it becomes non-linear and we have to get the snake out.  Perhaps 
those A.S. experts had some feeling for where extending that inverse 
relationship begins to fail reflecting reality.  Obviously a function of 
the size of the solids being transported, but they'd likely also have a 
good feeling for that size too.  Perhaps they knew from experience that 
testing a 2" line would show it too frequently stops up instead of 
transporting the solids.
   My tendency is to #1: trust the experts, and #2: be conservative 
because I don't want to be using my snake.  For me, being conservative 
here certainly includes using a pipe notably larger in diameter than the 
exit aperture of the fixture.

Joe


On 4/24/2016 4:51 PM, Reuben Deumling wrote:
> Except that carriage distance is inversely related to pipe diameter at 
> low flow rates. That's the whole point.
> Under the conditions I'm interested in, a larger pipe works against 
> the goal we're discussing here, which is why the 0.8gpf toilets mated 
> with a 4" pipe performed so disastrously. My question to the designers 
> of that study and to anyone here is why they didn't consider testing 
> with a 2" line?
>
> On Sun, Apr 24, 2016 at 4:47 PM, Joe Killian <kaa-ajk at sonic.net 
> <mailto:kaa-ajk at sonic.net>> wrote:
>
>     Reuben,
>       The American standard Cadet 3 toilet (a popular and very good
>     unit) has for it's exit aperture:
>     "Fully-glazed 2-1/8" trapway with 2" ball pass"
>       If there's a stoppage anywhere, you'd want it to be AT the
>     toilet, not somewhere down the pipe.  So a pipe substantially
>     larger than the fixture's exit aperture would be advisable.
>
>       With a macerater, a 2" pipe is acceptable, afaik.  ...If you
>     wanted to trade that complication for the smaller pipe.
>     Joe
>
>
>     On 4/24/2016 3:29 PM, Reuben Deumling wrote:
>
>         I have long wondered whether or when anyone would dare diverge
>         from the 3" standard drainline diameter as we get toilets that
>         use less and less water per flush.
>         Interpolating from this chart:
>         http://www.mpwmd.net/rules/Apr2008/pdfs/RegII/rule24_table1.pdf
>         I see that in terms of fixture units, a 0.8gpf toilet is now
>         at 1, which puts it comfortably within the same class as
>         sinks, which as we know do not require anywhere near a 3"
>         drainline. So..... does anyone on this list know if there is
>         any movement toward allowing a 2" drainline for a 0.8gpf
>         toilet? Or whether there's been any testing of this configuration?
>
>
>
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