An overflow system in the bathtub has an overflow port and has a drain pipe in connection with the overflow port. A threaded flange has a stub shoulder on one end which is fitted into a circular sleeve on the overflow port. The threaded flange has exterior threads on its outer surface and a thin diaphragm secured to the end thereof opposite to the stub shoulder. A large sealing washer embraces the outside of the circular flange on the overflow port and extends partially over the threads of the threaded flange. A large internally threaded nut is threadably mounted on the outer end of the threaded flange and compresses the sealing washer against a vertical flange on the port to seal the connection between the threaded flange and the port. A decorative cap is frictionally snapped into engagement with protrusions on the outer surface of the nut. The cap can be removed when needed to permit the plumber to gain access to the diaphragm to cut it open for fluid flow after the system has been tested for leaks, or put in place after the cut takes place.