Natura Drainable Pouch. The Natura pouches are compatible with SUR-FIT Natura Two-Piece Ostomy System which is ConvaTec?s most extensive two-piece product line. The SUR-FIT Natura and Natura Flange System signals a secure, accurate closure with a series of audible clicks". A simple snap-off, snap on design allows users to change the pouch quickly to match activities without removing the skin barrier from the skin.