A leak detecting device for a fluid filled vessel including a housing having a continuous perimeter edge sized to extend around an underwater surface, the housing forming a hollow interior, an anchoring attachment extending through an aperture in the housing for immovably anchoring the housing to the underwater surface, a resilient member secured to the perimeter edge of the housing and adapted to contact and form a seal between the housing and the underwater surface, and an inlet forming an opening through an entirety of a wall of the housing accessible from an exterior of the housing.