How do I bathroom / kitchen / extension? etc.

As someone who's had to deal with not enough drop on a wastewater pipe in the past, that bit of flexible white pipe terrifies me 🫣

Is it just temporary to keep things watertight?

@Soul bathroom looking good! Is there some sort of tanking/moisture resistant board going on or is that already moisture resistant board around the shower, or is that not even a thing thats needed?!