Thinking about a Toto Drake. It would go on the 2nd floor of my house so there's a 2 story drop from the toilet down the line to the ground and then about 15 feet to a 90 degree turn and another 35 feet or so to the septic tank, gradually downhill all the way. I'm wondering if a 6 litre flush as in the Toto Drake be enough to move things along. Naturally there would be other flushes in between with just urine. My grey water is separate from the septic tank so there would be no extra water going through from washing, etc.

Thanks for your input.