Backflow protection / Drainage required?

Building a single-family house on a slab foundation. According to the planner, we do not need any backflow protection or drainage around the house. The building site is located in a depression on a street that slopes upward from left to right. The property is to be filled so that the left side of the house is at street level. The right side is somewhat below the street. I am unsure whether it really makes sense to do without a backflow valve in the shaft and not to install drainage around the house, especially since the property also slopes slightly on the other sides. What do you think about that? For safety reasons, I would prefer to have a backflow valve and drainage. Who has a backflow valve with a house on a slab foundation?

Moin Moin

If all processes are above the backwater level (manhole cover), a backwater valve is not necessary.

I am also considering the drainage in the sand slab.
I will decide this on site with the excavator during the excavation of the pit.

Olli