Back to back toilets

I have an old house and would like to add a bathroom. If possible I`d like to create the new bathroom back to back with the existing one, sharing the wet wall. My question is how to install a toilet back to back with the existing one. Are there fittings available for 2 toilets on the same stack. My old stack is cast iron so I`m going to have to cut it off and install PVC. The venting shouldn`t be a problem but I can`t figure out the main connection.

Any help and stories of experience would be appreciated.

Plumbing Toilet

Is your home on a crawl space or a slab?

psolutions said:

Is your home on a crawl space or a slab?

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The bathroom is on the second floor and the new one will be too.

You need to use a double fixture fitting, and not a sanitary cross. And you need to be aware of the maximum length for a toilet arm allowed by your code.

The new toilets do not work as well with fixture crosses as the old ones.
The double santees do not work at all.

With the quicker flushing toilets, it's important that they are vented and plumbed in such a way that the gush of water from one does not go up the other arm to the other toilet.