No, because everyone sees different results on Google. For example, I don't see that. But to me, that looks like a hillside property - so it might make sense because of the sewage level. But why are there so many in the picture? We have a total of 4 bathrooms, but only two exits to the outside. As I said, I'm only interested in the technical aspect. In addition, those are KG2000 pipes in the picture, so very pressure-resistant - always better for something like this than regular KG pipes. : Every penetration of the slab is a weak point - with basement construction, this is possibly even more critical than at street level like with no-basement construction. With a basement, of course, you have pipes on the ceiling/wall - which can of course be boxed in.