Need advice on how to run sewer pipe from a new room ,trench is already been dug?

need pipe size and how deep the trench should be, A friend? left me with the job half done. Any addvise would be helpful THX SAL.Need advice on how to run sewer pipe from a new room ,trench is already been dug?
Lay the sewer pipe with a gradual slope away from the house,


.05 degrees per foot, join pipes together always checking slope.Need advice on how to run sewer pipe from a new room ,trench is already been dug?
A more standard slope spec is 1/4 per foot (I put a 1'; block on one end of a 4 foot level.





Size depends on what is connected to the line..


1 1/4, 1 1/2, 2 inch ID for sinks


1 1/2 and 2'; for tubs and showers


4'; for toilets





Combinations require upsizing





You need a complete reference book to do this job right.. You must know code and specs for venting, where and how to use traps, Where and how to use a sanitary tee vs a y fitting...





How deep is a matter of where you start and end and keeping the drain buried below the floor, all while maintaining the correct slope. You should shoot for at least 3'; below the floor (measured from the top.. or whatever the slab thickness is) where the drain comes up.. everything downstream of this will go lower..





With the trench dug.. it would be false economy to do this yourself unless you get a lot of information... hire a pro.