Pressure drainage (wastewater only)

You just have to make sure with the supply line that there is no pump chamber below the backflow level. Maybe the city means that too? By the way, the pump is not a backflow preventer because it is not firmly screwed to the riser pipe. It is only placed on top and presses against the riser pipe through its own weight with the seal. (At least with Jung)
Which shaft are you taking? Are you doing it yourself?

My pump chamber has a supply line DN160, then it is directly divided into wastewater DN110 to the house and DN160 continues to the overflow of the cistern (rainwater storage). The cistern inlet DN160 is then connected to the downpipes DN110 (house + garage), one inlet is oversized (DN160) and also serves as an emergency overflow.

That may well be what the city means. I will inquire about it again. That's a good idea from you. I am currently coordinating with a pump installer. It will probably also be a Jung. It could even be the same model as yours. I have now looked at it again on Jung's website. So the pump shaft has two inlets? DN 100 for the house and DN 160 for rainwater. You let the DN 160 run into the overflow of your cistern? We will also let the rainwater infiltrate into the garden. If I have understood correctly, I could then lay the DN 160 into the infiltration basin as an emergency overflow?! Is that correct?

Rainwater also through the pumps? The title only mentions wastewater. The overflow of the cistern goes into the shaft, not the other way around.

No, mine has an inlet and directly behind it a branch set, DN160 goes through, DN110 branches off. Here it is roughly put together. No idea if it is the same with the single system.

Ah understood. Thanks for your effort. That is a very good idea. I will take it directly to the planner like that. I will report back. And thanks again, that helps more than you think!!!