Abstract: A cylinder possessing an externally threaded lower end mating an internally threaded drain collar bore seated in the top end of an upright hub drain is threaded into the bore and the elevation of the top end of the cylinder elevationally adjusted with respect to the hub drain. A gasket is compressed between the top face of the drain collar and the bottom surface of a rigid plate which is then secured to the top of the upright cylinder. An annular interior corner of the bottom surface of the plate inside the periphery of the plate locates an annular gasket in the desired disposition. Location of the plate upon the top of the cylinder may be assisted by matching sets of locating pins and holes utilizing a cylinder with a closed top end and the plate may be secured to the top of the cylinder by a bolt passed through an aperture through the plate and threaded into a tapped cavity of the closed top end of a cylinder.