In the past I have posted the NY and Brooklyn DOB code for gray water systems.
It is a newer version of the NYS Plumbing Code of 2007 (the most recent NYS version). It is more concise than the new IPC (2009), which I can’t post (you gotta buy it). The 2007 NYS PC is almost identical to the 2006/07 IPC and not much different from the 2009 IPC. The attached file also looks better than the old Appendix C I posted earlier.
The good news is that gray water is getting a lot more attention by the ICC and IAPMO and they have actively addressed some technical issues which the gray water scene has brought up in the past.
This is important for Eco Brooklyn because we have a couple gray water installations coming up and want to make sure they are done above board. Of course you can do a little switch after the plumbing inspection. We call that green building civil disobedience. But we would rather gray water be completely legal, which it is (almost…).