I'm not sure if this was a bethel myth or not, but a rumor that regularly circled bethel was the "housekeeper whores" of brooklyn. Supposedly an entire floor of single guys, couples, and house keepers were practicing group sex and wife swapping. Almost the entire floor were eventually disfellowshipped and asked to leave bethel.
Like I said, not sure if that was just a legend, or if it actually happened. But EVERYONE knew about that story. It was usually talked about when talking about other bethel "secrets", like suicides and deaths of various bethelites.