I only have a 15 gallon black water with a direct discharge grey water, like all of the AS of similar size and vintage that I have seen.
I keep 3, 15 gallon blue-boys and hook one up to catch the grey water. I like the 15 gallon ones as they are not difficult to push up the ramp into the truck for hauling. Don't tow them!
at least not on anything but good pavement and at very low speed.
Very few places allow grey water to be dumped directly. when you can legally do it, dig a hole at least a foot wide and foot and a half to two feet deep. throw a little hydrated lime in the hole (keeps the vermin population down).
As black water passes the same outlet, there is a case to be made for considering that type of discharge as black water. Under most state and federal CFR 503B rules, mixed waste is handled at the strictest disposal level. That said, i doubt it would be enforced under most circumstances.
An interesting story:
I am a Regional Biosolids/Septage Coordinator in Wisconsin. As I live in Madison it would not be too difficult to figure out my name. Getting to the story---
---A number of years ago I was answering a complaint at a campground. I was accompanied by a County Sanitarian/Zoning Administrator. The complaint was sewage on the ground.
We me with the Campground Manager and went to the area that was identified by the complainant. The manager figured it may have been some sour grapes over a music dispute.
The Zoning Administrator was pointing out, to the manager, some recent grey water discharges under a trailer.
He was in the middle of explaining the violation of State and County Septage rules when I walked over near another trailer. All of this time the manger is saying how they do not allow that practice. When I was about 20 feet from the RV, and as I was pointing out where a past discharge had been----whoosh!
The inhabitant of the RV walked out the door a second later.....just like in the comedy movie...we were sort of staring at him and he said with somewhat feigned surprise --- What!---
We then had a conversation with the Rv'er, and the manager. No citation (over $800.00), just warnings along with a Zoning and licensing warning if it happened again
....guess what! While we were talking, yup--another whoosh!
Sometimes you just can't seem to get out of there and just break even. actually we issued another warning and promised another visit - without warnings of either our coming or warning about discharges.
They had an old AS on blocks at the campground. It was on blocks but used a a rental. I was left with an impression it was for sale. I already have my own money pit for a hobby.
Check your state or Reservation Rules. Be a good neighbor. Giving out citations does not make anyone's day. I can buy a couple of blue boy totes and lot of gas for making blue boy dump runs for $800.00.