I have just aquired part ownership in a 1978 Oday 28 with an OMC Saildrive and have concern about the lower water flow from the exhaust even a higher RPM's. After reviewing the OMC manual, I see how I can do a fresh water flush at the dock with the engine running but what I would like to also do is a fresh water backflush through the impeller type pump located in the gear box to the outside through the raw water intake (without the motor running). The plan would be to disconnect the hose from the water supply valve and connect a water hose to the valve and force water back through the pump and out through the gear box openings to clear any debris. Does anyone know if this will work. My concern is the impeller pump will not allow a reverse flow.