A manifold for collecting a tissue sample with a medical waste collection assembly. A base portion of a housing is removably engaged with a manifold receiver to provide a suction path from an inlet fitting receiving a suction line. A tray may be removably positioned within an accessory sleeve. Locating features facilitate defining a gap between a base portion of the tray and a lower barrier of the accessory sleeve. The tray may include a control surface to move the manifold between a sealing configuration, and a bleed configuration in which a second suction path is provided through the gap and below the tray. A backflow prevention valve may be disposed within the suction path between the tray and a filter element. Methods for collecting the tissue sample are also disclosed.