Draining Grey Water
A friend of mine has recently purchased a used trailer that will be "permanently" parked at a seasonal site. It hasn't been delivered yet, but when it is, they have drains that can accept grey water only, but need to rely on their holding tank for black water, and get it pumped when needed. They don't expect to use the black tank much anyway, because bathrooms are provided on site.
The question is, how do you hook up the grey water tank to the drain without risking getting black water in it too? I know they can keep the black valve closed and use one of the adapters on the single outlet that allows them to attach a standard garden hose and feed that into the drain, but that's not a 100% guarantee, since many valves leak over time. Should the grey line be cut, and adapted to go directly into the drain, and then cap the side that connects to the black water tank? Should the "low point drain" be used?
What do others in this situation do?