toilet drain 3" or 4"?

[zxed]

question about my toilet drain.... i want to know if there is any specific reason if the following is done (see image)

i can guess that the 4" allows for a smoother flush...

the current setup is for a 14" toilet rough, the new toilet is a 12"..

since i need to move it back., should i simply move it 2 inches back, or should i re-create with a 3" drain and 4" to 3" flange?

[Redwood]

I'm not understanding your post.
Are you planning on having a 4" line at the toilet that then goes into a 3" line further down?

[iminaquagmire]

Use a 3x4 reducing closet bend. It'll have a 4" inlet and a 3" outlet. Makes setting the flange much easier since you use a 4" inside fit flange. I would change it for that reason alone. That way you can leave the pipe long and tile up to it. Then when your floor is done, you can trim the pipe flush and install your flange on top of the tile for a perfect, fully supported flange. I wouldn't use any reducing couplings anywhere.

[zxed]

Use a 3x4 reducing closet bend. It'll have a 4" inlet and a 3" outlet. Makes setting the flange much easier since you use a 4" inside fit flange. I would change it for that reason alone. That way you can leave the pipe long and tile up to it. Then when your floor is done, you can trim the pipe flush and install your flange on top of the tile for a perfect, fully supported flange. I wouldn't use any reducing couplings anywhere.

i like the idea of triming the pipe flush after all the flooring is done..

so something like this

so once i attach the 3" to the horizontal waste drain, i will still need to drop in a 4" pipe for the top so that it sticks out high enough for me to cut flush later correct?

[zxed]

I'm not understanding your post.
Are you planning on having a 4" line at the toilet that then goes into a 3" line further down?

that is what is there right now. i was asking if that is fine or if i should change it 3" all the way

[Redwood]

It should be 3" all the way!

[zxed]

It should be 3" all the way!

any clue why they (original home construction back in 1979) would install it the other way? 4" turning into a 3"

[hj]

For the same reason I still only do it that way. It makes a better installation, but I use the 4x3 hub and spigot bend with 6" long riser. Then I install a slip on flange that slides over the pipe and down onto the floor, and if necessary cut the riser off to fit AFTERWARDS

[Redwood]

Oh your only talking about 4" right at the toilet and then 3" at the end of the bend...
Thats okay.

[zxed]

For the same reason I still only do it that way. It makes a better installation, but I use the 4x3 hub and spigot bend with 6" long riser. Then I install a slip on flange that slides over the pipe and down onto the floor, and if necessary cut the riser off to fit AFTERWARDS

Thankyou all.

Is a hub x spigot also known as a hub x spg or 4x3 street 1/4