Double Wye for Back to Back Tolets?

Double Wye for Back to Back Toilets?

I a home owner doing my own plumbing of back to back toilets - can I use a 3" double wye with 45 degree ells with a 3" by 4" ell which then has approximately 12" of 4" pipe going up through the second floor to the toilet flange? I read in the IRC that sanitary crosses cannot be used for back to back toilets unless the developed length between the closet bend and the sanitary cross is 18" or greater? Any light you can shed on which fitting to use is appreciated.

Most closet bends tie into a tee wye. I'm not sure why you would do 4" from flange to a 3" stack(if I'm reading that right). I know some people think its a good idea but i tend to do 3" all around or 4" all around. I think it looks nicer. I would do Off 3" stack with double tee wye 3" 90 up to flange on both sides. I know there are alot of plumbers on here that will say other wise but thats what i have seen mostly and the other way is not the norm in my state Mass.

If you place a sketch, or pic on what you have and or what you want to do you will get more help.

Thanks Patrick88,

I will take a picture and post it this afternoon. I have trouble describing plumbing details.

I will take a picture and post it this afternoon. I have trouble describing plumbing details.
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If you don't know the proper terms you could end up saying the wrong thing and making matters worse for your self. With a pic or sketch of what you want it is simpler to see what you want

Pics of Double Wye Back to Back W Closet Plumbing

Here is a photo of my back to back water closet arrangement. I had to work around 12" deep floor trusses. Please advise if the double wye won't meet the IRC code when used this way. Thanks all.

I cant see where any inspecter would have a problem with it.