Abstract: A novel device for use in combination with a coupling device for coupling a drain hose to a drain pipe outlet from a waste holding tank of a trailer is provided herein. It includes a hollow cylindrical section to which that drain hose is adapted to be clamped. An aperture of a specifically-recited size, and located at a specifically recited site surrounded by a hollow shaft covered with a slitted elastomeric cover, is provided in the hollow cylindrical collar for the insertion therethrough of a flushing hose so that the flushing hose is insertable through that slit and into the aperture, through the hollow cylindrical section, through a blade valve which is disposed in the drain pipe and directly into the waste holding tank. Flushing water may thus be directly injected into the waste holding tank while leakage of flushed water from the waste holding tank through the aperture is minimized. A circular ring-like flange is secured to the end of the section which is remote from the drain hose.