Our low-tech gray water filtration system. There is about a cubic yard of drainage/mound sand spread underneath the barrel. Then the barrel is filled with - from bottom to top - one-third sand, one-third gravel/small stone, and one-third larger rocks. Then a screen is tied over the top of the barrel to filter out larger food particles as water is poured in (the screen is periodically shaken off into the compost). Around the outside of the sand mound is nice mixed soil, where water-loving plants will grow and help filter and dissipate the gray water.