Tubby, if Western Australia have similar laws to Qld & I feel under the Environmental Laws they must. you would have to have a Site Assessment done by a Soil Engineer & then employ a Fully Licensed Plumber to install the System as the waste drainage is classed as Sanitary Plumbing & therefore regulated under the Law. You see Tubby when you deal with Grey Water, if it is stored for more than 1 hr it becomes Black!
Most people urinate in the Shower, Women tend to have periods & people also blow their noses & wash off Faecle matter which goes down the shower.
When a person cleans their teeth they spit out pathogens & blood.
When a person washes Clothes the clothes have all sorts of grungy stuff on them, Underpants & undies have Skidmarks & Nocturnal stuff on them.
So you see it is not only grey but alive. There are laws about the safe application of this untreated primary effluent.