I am adding a bathroom in my attic and would like to make sure that my drainage plan is sound.

The plan is to have a lav, toilet, standup shower (fixtures in order to the septic). I plan on having a 2" vent at the beginning of the line (lav) straight up to the roof as well as a 3" vent after the 3 fixtures when the waste drops to the basement.

From the lav (2"), water will flow horizontally about 3' to a 3" combo where the toilet will feed. 3' after the 3" combo, the shower would also feed into main line. From this point the waste would flow down a 3" vented sanitary T to the basement.

Here is where I am unsure what to do given all else is good.

I have a ~10' drop to basement due to existing shelve that I need to work around on the 2nd floor, I have to drop it about 1' then flow horizontal for a couple of feet then down 9' to the basement line. My question is... Should I just treat this 1' drop as a normal vertical drop and use a combo (cleanout) followed by a santiary T to the longer 9' drop or can I use a combo and a long sweep 90? Or even 2 long sweeps to just allow the waste to flow a couple of feet before dropping to basement? What would be the best solution here given all else is sound?

Finally, once to the basement, the waste would drop into a combo (vert to horiz) with a cleanout and then tap into the existing lines on its way to the septic.

Assume the lav and shower will contain traps. Hope this is clear enough. Any help would be greatly appreciated.