Yeah, there was a discussion a few weeks ago about dishwasher back wash and after looking into it, it seemed like a bunch of states didn't require it. The vast number of different ways that states go about their plumbing codes makes it damn near impossible to discuss code on the internet regarding the United States. IPC, UPC, NSPC, and a bunch of variations based on them, along with some states using code per municipality. You may as well pile into a clown car as to try to give advice based on code over the internet. That's where my facetious comment above came from. I see so many folks citing code here that may or may not be relevant to where someone lives. It gets old.