Abstract: A gasket assembly is provided for coupling the drainage outlet openings of a bathtub and of a plastic liner installed within the bathtub for renovating the latter. The gasket assembly includes a hollow cylindrical body inserted in the space between the bottom wall of the plastic liner and the bottom wall of the bathtub, and having flanges at its upper and lower ends for making sealed connections with the drainage outlet opening of the bathtub and the overlying outlet opening of the plastic liner. The gasket body is made of elastomeric material and has an accordion-pleated side wall so that it is stretchable and compressible and therefore adaptable to bathtub installations of differing sizes. One-way valve means are also provided on the gasket body for draining out water which may accumulate in the space between the plastic liner bottom wall and the bottom wall of the bathtub.