Prefered Drain Pitch

[shaken-n-stirred]

In new construction I have the septic line leaving the crawlspace at say 24 inches below the bottom of the floor joints. I expect to have a four inch ABS pipe run straight back from that point with proper 1/4 inch per foot pitch. That pipe will run perhaps 10 to 15 feet back into the crawlspace. Into that four inch pipe will enter three 3" pipes coming from different areas of the house. At least one of those runs is long enough such that the run will drop down into the crawlspace and turn immediately (high up at the bottom of the joists) to run to the 4 inch pipe and would nicely flow at the 1/4 inch per foot slope. At least one of the other runs will be closer to the 4 inch pipe. So the question is; is it better drop the line down into the crawlspace, and immediately turn toward the 4 inch pipe (again, high up on the joists), and then at the 4 inch pipe increase the pitch to drop into the 4 inch pipe, or should the drain be dropped lower at the point it enters the crawlspace and maintain an even pitch all the way to the 4 inch pipe and into the 4 inch pipe?

Thank you.