This has nothing to do with cisterns, but...
The approved grey water system on St Barth works like this:
1) from lowest point in the villa into septic tank which has a aerator to break down solids
View attachment 23813
2) by gravity into a secondary tank.
View attachment 23814
3) pumped through filters (changed every other month) up the hill, some goes into a drain field which percolates into the soil of coarse sand.
View attachment 23815
4) by gravity down to water the garden.
Voila----as long as this system is
well maintained, there is no odor whatsoever and the jardin is green or vert!