New main drain line in basement

[mwendig]

I am installing a new single story, stick built, modular home. It is a duplex with two 3 bed/2 bath units in it. Full basement underneath on private well/septic. Upstairs is done by the builder with all utilities stubbed to the basement.

Because it is modular it has a center beam in where the two pieces came together with plumbing on both sides. Therefore I am going to run main line from the corner where the septic comes in up both long sides of the basement and bring each fixture's drain down the joist cavity dropping into the main line. (No joist drilling) I think I am on the right track but I wanted to check on a few things:

-Main drain size-I am planning on 4" sched. 40. Is this overkill?

-I plan on using sweeps connected to sanitary T's for the drops connecting the joist bay runs to the main line. Any issues? Any reason to use a Wye instead?

-There are vent lines ran into the basement from the attic, I plan on hooking these up to the main line the same as the other drain lines but using a regular T. Issues?

-Future maintenance/fixture replacement ease-I plan on doing the following
*Plenty of clean outs
*Sinks will have trap adapters that the trap can be loosened and slid apart for cleaning/replacement

Thoughts appreciated!
Thank you.

 

[Terry]

On the horizontal:
You can run three bathroom sets on 3"
The forth, where it comes in would become 4"

You use wye fittings for waste on the horizontal. A santee splits the waste, and it winds up going two directions. Not good.

Helpful Plumbing Hints for Residential Construction by Bert Polk Plumbing Inspector Lincoln County