Odd trap / drain depth question.
As I noted in a different thread, a licensed plumber will be plumbing (at least DWV) a bathroom addition for me.
In the drawing below, there is a soon to be poured concrete slab (in green) and also a soon to be poured foundation (in white).
In order to maintain access to the second port of the septic tank, there has to be a slight "crawl space". As it happens, the shower drain will also need to run through this area.
When we pour the foundation, we will need to provide an opening in the foundation for the shower drain to meet up with the tub drain.
My question is: What is a good distance (vertically) from the bottom of the shower to the port in the foundation?