I did see that and agree it's overkill but was referring to this thread
on this FR site. The reference was vague, which is why I asked. It sounded to me like the overflow was passive but would have to be one-way.
I guess I could inquire with the member who posted that comment but I only just found it again.
EDIT: I tried to reply to the thread but it's ancient, and closed. Also, the member (Triguy) hasn't posted a message since August. I sent a PM in the hope that he's still around. Maybe others here will recall that topic and know what he was referring to.