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

[Joe Killian]

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?