I've been cogitating on this for a couple of years now. I've been supposed to get my composting toilet together for months now ::blushing:: but other things keep interfering. Although I do have the five gallon bucket and the wood for building it.
In any case, this is how far I've gotten and what I'd suggest.
First, download The Humanure Handbook. Lots of people here do sawdust and composting toilets --- you will be deluged with good suggestions.
Second, for grey water --- be aware that hot water is not great to dump on soil. So cogitate on some way of cooling.
In addition, you don't want grease dumping out back. Start now working on what to do with all the grease from foods. I have several coffee and other cans I keep for this purpose; I use a large coffee can for unusable grease and smaller ones for bacon fats and other greases I can use for flavoring and for critters!)
There are things you can attach to your pipes which act as grease capture thingies. They're not so expensive (maybe $50-70 each). I plan to do that.
Check on the rules in your state for composting toilets and grey water management. It helps A LOT to know what you may or may not be looking ahead to, in terms of regulations, etc. Fortunately, Oklahoma is fairly liberal on these issues
--- it took me months of digging around to come to that conclusion, but knowing that freed me up quite a bit.
Read as much as you can about grey water! There are a lot of systems out there, some more useful than others --- you will need to do some adapting for your purposes, whichever you choose.
