help designing passive grey water system

I'm in southern Honshu, Japan. I'm designing a grey water system which needs to deal with kitchen/washing water for 2 people plus a lot of guests I don't know too much about the plant types to use.. The only thing I have some idea of is water goes downhill... so I need start at a high spot and descend with some kind of biofiltering sections until I reach the drainage system. Everything on the island unfortunately drains to the ocean... so we'll move towards more biofriendly soaps etc. but this won't be perfect so I need to figure a hardy sort of micro-organisms that can break down regular soaps and oils. I expect to use a composting area in line with the greywater system, so there will be a good source of organisms and I know soaps can be broken down this way, but I don't know how to create optimal conditions, though heat is an obvious need.. Any info on how to get this thing going would be helpful.. I have like 325 sq feet to do this in, but only maybe 20" of fall to play with. I also will be making charcoal which I will test out as final filter field probably mixed with compost and maybe some stones to add pourousness. Bamboo grows like mad here so I can use that pretty liberally and expect it to increase the hardiness and activity of my numerous tiny friends. Thanks

Try to get a copy of Art Ludwig's book, Create an Oasis with Greywater. At least start by reading all the relevant pages on his website, http://oasisdesign.net/ and then get the book. It's really worth it and will help you avoid a lot of the common mistakes people do when designing greywater.

My experience with treating greywater in topsoil is that it didn't take any specially hardy organisms to deal with soap. The topsoil organisms just dealt with it, immediately. Ludwig's book says topsoil is one of the best and easiest ways, as it's well aerated and has a very diverse community of organisms. But there are many simple systems that will fit your needs, which don't sound excessive.