ᐅ Constructing an Exterior Concrete Staircase to the Basement?

Hello,
I have a basement door leading outside in my house. I need to build an external stairway to the basement here. I was thinking of pouring a concrete foundation for the basement stairs and then placing a precast stair unit from a concrete factory on top. Now, the problem is that the house’s sewer connection runs underneath the stairway or the slab. Is there anything I need to consider, or can I simply pour concrete over it, meaning a clean layer first and then cement on top? There is also a branch pipe from the sewer connection here that is supposed to be embedded as a drain within the foundation.

Ah, ...and what does the drainage plan show?
How is backflow protection supposed to be ensured?
Is it even allowed to discharge rainwater into the sewer system?
This should be clarified first before proceeding further!

The drainage plan shows a floor drain there. I cannot direct the water anywhere else. The rainwater is intended to be diverted into a cistern, and it is from the roof as well, but it cannot be done from the basement because the cistern is located considerably higher than the floor drain. The backwater valve is installed further forward towards the street, before the cistern.

Since the staircase will probably settle slightly, make sure that the drain pipe is not rigidly embedded in concrete. Especially leave a gap of 2-4 cm (1-1.5 inches) above the pipe.

From a drainage perspective, it is not well designed... Does the cistern have an overflow into the sewer?
Would it be possible to cover the basement stairwell?
How far along are you with the construction?
Was the basement stairwell not taken into account in the slab? Then there are foundations! Is it surface water or groundwater? If none is expected, I would prefer to accept some settlement rather than create a fixed connection with the basement wall.
Why do you want to install a precast staircase?
Have you considered how it will be backfilled? :-? Also, the earth side needs to be retained. It would be easier to cast concrete on site... and certainly more cost-effective. Has the price of the stairs been calculated including transport and crane?
Think it over again. Excavations, foundations, and retaining walls have to be done on site anyway, so why use a precast staircase if there is a risk of additional settlement at the upper foundation because it cannot be properly backfilled and compacted?

The cistern has an overflow connected to the sewer. The thing is, our house is located on a slope. The cistern is positioned slightly higher on the hillside because there is a connection to the boiler room for the domestic water system. I have also considered adding a roof cover, which could then be connected to the roof downpipe.

However, I still wanted a floor drain in front of the basement entrance door. We are close to moving in. The staircase was not included in the foundation slab. This has upset many people already. I had to have the area excavated further afterwards. We are building with a developer who only did what was contracted. They could have offered to take care of it at the same time, but I guess I didn’t think of everything either. I didn’t want a connection to the basement wall because settling could cause cracks in the wall. A precast staircase was recommended to me, as its surface is supposed to be better than that of cast-in-place stairs. However, I haven’t requested a quote yet. Surely, looking at it, cast-in-place stairs might be better. I will ask about that.