Use a helophyte filtration (constructed wetland) system, like:
In essence, you need to let the poop and stuff go to the bottom then have the plants filter out the chemical and biological contaminants. Finally the treated water is directed off of the site (potentially into the next level of filtration). So, a three step program:
https://www.instructables.com/Filter-your-Laundry-Graywater-with-Marsh-Plants/
https://www.treehugger.com/how-use-grey-water-garden-4863690
https://www.youtube.com/watch?v=uZXMOfkrZYA
https://www.doityourself.com/stry/activatecharcoal
Clean water can generally be viewed as what we collect from collection infrastructure. However, treated greywater can be used in the same regard.
Check out the callout in previous section, the main reason for not trusting these systems is that they don’t have disinfectant stages.