I want to create a new bathroom behind an existing one. I need advice on how to use one toilet plumbing drain for two toilets.

Here are the facts:
In the existing bathroom, all of the plumbing is in one wall, which runs toilet, sink, bath.

The new toilet will be directly behind the old one in the new room, which is being created in a hallway.

This space is on the third floor of an apartment building in New York. Creating new plumbing lines from the basement is out of the question.

I am told that it can be done if the 2nd toilet is elevated sufficiently. Does anyone have experience doing this?