Abstract: An apertured mounting unit comprises a deck sheet with a top and a bottom surface, the deck sheet has a cross-sectional edge defining an aperture. A non-porous seal member abuts the edge, the seal member has top and bottom surfaces. A sink with an upper circumferential flange may be removably mounted on the bottom surface of the deck sheet, with the flange in sealing engagement with the seal member. The flange cooperates with the seal member and with the bottom surface of the deck sheet so that the flange is brought into sealable engagement with the seal member when the flange is biased against a stop that is fixed with respect to the bottom surface of the deck sheet.