Thanks. I should have read what I wrote...wasn't clear. I have heard of systems where gray water supplied toilets but I may be mistaken.
The concept I am pursuing is dual supply and dual output. Supply would be well water for sanitary/human consumption and rain water for toilets and non-sanitary uses via a cistern (I thought gray water might possibly be used to supply toilets but if it can't be sequestered, then no).
The output of the system would be sewage to a septic system and gray water emptying into a duck pond with fish and aquatic plants to clean. Duck pond supplies garden with irrigation. Anyway, yes, gray water to the garden via duck pond.
The question should have been how to set up the plumbing to pass code but be easily converted to a set up that segregates the gray water out from the sewage and allows the supply to come from two sources as well.
Sorry wasn't well written (distracted by work)