A flexible membrane is situated within a rigid or semi-rigid cap. The edge of the cap wall is adhesively fixed to the tissue surrounding the stoma. The interior of the cap is pressurized to press the membrane to seal the stoma against the discharge of solid and semi-solid waste. Gas escapes through a vent with a filter element. The cap can be pressurized by an external pump or an integral pump member situated on top of the cap. A relief valve prevents over pressurization. A collection pouch can be provided as part of a device. The device can be removably mounted on a standard two-piece faceplate.