When we put in a new septic system at our Adirondack cottage, since the new line to the tank passed right behind our RV parking site, we blew an extra $20 to add a sanitary 'T' and a 4" clean out for dumping the RV tanks. The only "issue" we had, was that the plans we submitted for the permit called out an "RV Dump Site", but the inspector changed it a "4" Clean Out". He laughed and said he knew what we would use it for, and we knew what we would use it for, but the code doesn't allow us to call it that. So we happily dump in our "clean out" instead...