Very helpful ,John, thank you. I had seen - and read the majority of - the first thread, but hadn't run across the second. Having read the second one now, I have a question about Jason's response to you. He said ...
It is tied into the plumbing line under the bath vanity that vents out the roof of the camper. This plumbing pipe is used to allow air to vent out of the system for proper draining. It is not tied into the black tank, but the black tank flush port is on the outside of the camper. No one can run water into the black tank from outside because under the dinette seat inside the camper we have an inline shark bite valve that you will leave closed to prevent this from happening. The vent is also connected so if they did fill up the black tank it would overflow into the vent pipe and drain into the grey tank.
Is he saying that the inline shark valve is between the outside flush port and the black tank? Or between the black tank and the outlet in the bumper? I can't see a shark bite valve under the dinette, but I don't quite know what I'm looking for. If he meant the the former (which I think he meant), it doesn't affect my plan to re-purpose the black tank as an auxiliary gray tank. However, if the latter, it seems it would prevent me from allowing gray water to flow "backwards" into the black tank.
Having said that, it may be a moot point though, because it appears to me that the black tank sits higher than the gray tank. In that case, water from the gray will never equalize itself UP into the black tank.
Anyone have comments?