Abstract: A drain hose flush adapter, system, and method of use for cleaning or flushing hoses and tubes such as those used to drain waste water sewage and holding tanks is provided. One end of the adapter may be connected to a source of flushing fluid, and the other end of the adapter may be connected to a waste water drain hose, so that the flushing fluid flows through the adapter and into the hose with minimal leakage. In addition, the connections can be secure enough so that the operator is able to manipulate the hose and complete the flushing, with a low risk of being subject to fluid leaking from the adapter. Thus, for instance, the invention could be used to drain hoses used to drain black and/or gray waste water holding tanks of recreation vehicles, motor homes, travel trailers, campers, airplanes, and boats.