[BB_TX]

You are correct it is government mandated. And for good reason. To protect the public water supply systems from contaminated water. A water system with access to any contaminated water source and in turn connected to the local public water system is required to have a device to prevent contaminated water from being siphoned from that contaminated source back into that public system. Although highly unlikely it would ever happen thru an RV black tank flush system, it is remotely possible. And no matter how remote, if it is possible sooner or later it will happen.

When a public water system loses pressure, it pulls a vacuum on those water lines and sucks water back into it from any open source.