Toilet Waste Line - Looking for NYC Building Codes for Required Dimensions.

A toilet can be served by a 3″ line or a 4″, but there may be other considerations, and your plumber can discuss that with you. I’ve had plumbers say a 4″ is required, but this rule changed when toilets were limited to 1.6 gallons per flush, so if it’s a new toilet 3 should be OK. Long or complex runs might be better with the larger pipe. Some people say with less water, the smaller pipe is less likely to clog since the water level will be higher, others say that’s hogwash.

hkapstein

in General Discussion 4 years and 1 month ago

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CG_ups | 4 years and 2 months ago

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Hi All, does anyone know where to find the building codes for the required dimension of a toilet waste line for an upper floor bathroom? This is the waste line lead pipe going from the bottom of the toilet to the building waste line. I need the sizing required of the opening by the toilet flange.

Thank you!

andriywww1990 | 4 years and 2 months ago

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i think all toilet waste lines are 4″. Now you get to here the backstory as to how i know that:

i was working in a building on 57th when i first got to NYC. the plumber came to look at a leaking pipe in an office ceiling (above a drop ceiling) of a WWI era building. My boss and the plumber said “it is a 3″ line, so it must be the roof drain”. i said, “no there is a bathroom straight that way and i think it is a poo line:” of course i lost that battle and went about my business. the plumber cut the pipe and was up on a ladder, looking at the pipe when he heard something coming down the “roof drain line” on a perfectly sunny day. he could not get out of the way fast enough and ended up with toilet paper and something else all over him. (they had added a restroom and had tied it into to the roof drain line).

there is a moral to this story and that is that most people did not care what the code is or was but you should care for the sake of the pl umber who comes a long sometime after we have all expired. from that day forward, i have been under the impression that it is a 4″ line.

agdipierro

in General Discussion 4 years and 2 months ago

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Go to Section 709 of the NYC Plumbing Code. Look at tables 709.1 and 709.2. A bathroom group, as defined in Section 202, has a drainage fixture unit value of 5 or 6 depending upon the flow of the toilet. A drainage fixture unit vale of 5 needs a minimum 3″ diameter waste line. A value of six requires a 4″ line.