What auntyjack was attempting to convey was that in her community in Australia, the greywater (sink, shower, washing machine) is pumped into the local water systems (is sodium lauryl sulfate really that biodegradable?), while brown(?) water, that is, poopy water, is handled by a waste treatment facility. Where, depending upon the wealth of the area, they MAY attempt to treat heavy metal/organic contamination or they may just ferment it for a while then release it back into the local ecosystem, or even several miles out into the ocean.
I would suggest not dumping ANY chemical waste down your drains, though.
Well, besides maybe acetone, ammonia, muriatic acid, sulfuric acid, sodium hydroxide... can anybody name any others that are probably OK to put into public sewage lines in small amounts?