I am going through a major renovation in my house which involves excavating 7'6" basement and pouring seismically strong 15" slab as a floor. The house is pretty high on the hill and something like 50' from the property line. I have a sewer line currently going under floor joists and in the middle of the space that will become a basement. So it will be above one's head after basement is done. In future, I want to consider getting a small powder room (toilet + sink) in that basement. So I decided that I want to reroute the sewer line under the slab using trenches excavated for drainage. Those trenches will be something like 6'-7' below the grade line.
Since we are on a small hill, per measurements, there should be enough slope for this sewer and lateral to be below the slab.
I will have plumber to do it but what are the things that I should look especially carefully considering that the entire house drain will go through this line and that fixing it may be ridiculously expensive?
Should I require specific access boxes installed at every join of the pipe? If so what is the recommended size and kind? How should I evaluate the quality of all connections? I think pressure test is required anyway.