I am replacing my red sea max s650 stock return pump with the Neptune COR20. I would like to keep my stock as backup. Does anyone know what the return line hose diameters are? Also, There is a union connection into the main down pipe, what is the thread size of the connection? My idea is to keep the stock pump with the hose attached and just disconnect at the main down pipe union for easy replacement is needed and buy new for the new pump.