Well, technically we're under three codes if you will. The state code, the city code, which is more restrictive in some small areas, and the waste water folks in the city. They have ammended such that we have to use ductile more often and can't use PVC on sewers except under very certain and highly expensive circumstances (set on 12" of sand, sch 80 pipe with sch 40 fittings, covered in 30" of sand before tailings can go back in the hole, etc).
I feel for you folks that must deal with multiple AHJs and codes. We deal with about 6-8 max, and there are some quirks with each, but nothing as major as a completely separate code. Just more restrictive ones.