Here's a quick sketch of my waste line. The main line is 3" to the Septic with the kitchen, laundry, and bathroom connecting to it. I wondering if I'll have any problems with the toilet waste draining with the 45 degree bend? it's a single story and all of this will be in the crawlspace.
(https://i44.photobucket.com/albums/f11/retiredmarine1/puumbing_zpsnkjgyxqs.jpg) (https://s44.photobucket.com/user/retiredmarine1/media/puumbing_zpsnkjgyxqs.jpg.html)
It basically looks good to me. The main line should be 4", though (the hole in the septic tank should be 4"). I would keep that line at 4" until you get to that toilet.. you can even run 4" to the toilet itself it you're worried about it, - toilet flanges typically glue outside 3" or inside 4" line. I personally oversized everything, I ran 2" to sinks/tubs/washer then put a bushing in when I came out of the wall. In addition to helping with clogs, it makes any venting problems go away too.
Also a shower drain is 2", a tub drain is 1.5".
https://www.amazon.com/Plumbing-Pros-Rex-Cauldwell/dp/1561588172/ref=sr_1_1?keywords=rex+cauldwell+plumbing&qid=1559686693&s=gateway&sr=8-1
I thought this book was great for plumbing. He really spells it all out and doesn't get lost in the code... which the code was pretty indecipherable to me. I basically did what he said and have not had a single issue (yet :))
Thanks Nathan! I'll check that book out.