Floor-level shower installation situation

Hello everyone,

we would like to install a walk-in shower at our place. However, I am wondering if the installation situation allows for it:
At the edge of the shower area, there is a DN100 wastewater pipe installed, to which the siphon of the walk-in shower would have to be connected. There is only one toilet connected from the same room.
Since the DN100 wastewater pipe already protrudes above floor level, I wonder if this will work or is allowed?
As soon as the DN100 pipe is completely filled with water, water would run out of the shower...
But this is probably never the case in practice, or how high does the water level rise when the toilet is flushed?
Would that work?
I hope the attached picture clarifies the installation situation!

Is it about a new construction and planning or about an existing condition and "retrofitting" of the walk-in shower?

Is it about a new build and planning or about an existing condition and "retrofitting" of the walk-in shower?

It is about the existing condition!

To be honest, I don't fully understand the drawing, but basically the wastewater pipes are never completely filled with water (unless they are clogged), but always contain air as well (which is why they need to be vented depending on their length). How full or empty they are is referred to as the filling level – this should be at least 0.5 (i.e. pipe half full), and usually should not exceed 0.7.

Branches, however, may only be introduced at an angle of 45° (seen horizontally) and with a slope of 15° diagonally from above into the continuous (horizontal) pipe – so this will be quite difficult to impossible for you. According to your drawing, you don’t even have enough height difference to create a slope between the siphon and the pipe.

Can you break up the floor to lay the DN100 pipe deeper?

For the connection of the shower drainage, you can go down to 50 if in doubt. It can also be connected to 100. I just wonder what the appearance is like if the 100 pipe is higher than the floor? Do you get enough slope by then?

Somehow I still lack a bit of imagination. Can you upload a photo?