Shutree
I would only install a grey water tank if you were considering using the water for irrigation., and you would have to keep the tank pumped every couple of days otherwise it will really smell. I had that issue in AUS.
Having the grey water into the one tank helps the sewer lines to flow better.
Unfortunately I am on a very small block and the treated waste connects to the street pipe (basically a large storm water pipe) I would have preferred to install soakage /evaporation trenches but no room.
Importantly
The system has traps on all fixtures to stop the smells from coming into the house and it is thoroughly vented which will allow the waste water to get away without any effort.
I also included a cleanout at the head of the line and an ORG (overflow relief gully) at the base of the line. If I get a blockage then the s--t will come out of the ORG and not the downstairs shower.