Systems, methods, and devices are disclosed that involve a fistula-isolating device for use when reduced pressure is applied to a wound bed having a fistula. In one instance, the fistula-isolating device includes an adjustable passageway member and a perimeter member that contracts under reduced pressure and that automatically accommodates wound beds of different heights. In another instance, the fistula-isolating device involves a body shaped as a frustro-conical body that is readily sized for different depth wound beds. Other systems, methods, and devices are presented.