View Full Version : 3" OD to 4" Flange?

05-29-2007, 10:07 AM
GC Here, plumber roughed a 4" OD PVC waste.

I have a 3" flush valve Jacuzzi toilet and do not want to reduce inside the waste since that will make the opening too small.

Is a outside mount 4" flange safe? In other words, solvent welding the flange to the outside of the stack, is that safe against water leaks?

05-29-2007, 01:39 PM
Perfectly fine. The average toilet's internal pathway is often only a little over 2" or so. The only thing the seal does most of the time is keep out sewer gas. It only has to deal with leaks if it gets clogged up or maybe a little splash.

05-29-2007, 02:36 PM
Sounded like you were describing a gasket. Basically the pipe is 4"OD, which means less than 4" ID, and putting a smaller pipe inside of that would reduce it down to almost 2" which is not code.

Therefore, I guess I need to solvent weld the 4"ID flange to the outside of the stack (versus the inside). So, I know the solvent weld is strong, but just wanted to make sure under the pressure of the flush since the pipe configuration would be somewhat against the folow of water. Thanks!

Gary Swart
05-29-2007, 04:19 PM
I think your waste pipe is 3". You are correct about putting a flange inside of that because it will reduce the diameter of the pipe too much. You can put a flange inside a 4" pipe OK, but for 3" it needs to be one that fits over the outside.

05-29-2007, 04:22 PM
within a day or two i predict hands-on experts will give you more of what you want. Measure ID and OD again and post it. Know your numbers.

Four inches is a lot bigger than needed, and three inches is fine, just fine. Bigger is not always better, because too big is not good. Three inches for a single toilet is just fine, and not too small, never ever ever.

About what to put inside (or outside) wait for the people who set toilets for a living.

edit: looks like Gary Swart beat me to it. And he is one of those guys, who knows ...

05-29-2007, 06:45 PM
ANy flange you put on the outside of the pipe (whether it is a 3" or 4" pipe - they are measured by the inside diameter in waste pipe) will be fine. You don't want to use an inside mounted flange on a 3" pipe unless all other choices are (nearly) impossible. On PVC or ABS, you aren't really gluing things...the cement actually liquifies the outside of the plastic, and welds it together. Done right, it does not leak, and will be a bear to take apart...don't worry about it.

05-30-2007, 07:47 AM
Thanks All.