Hi All. I believe having read your posts leave it to next winter, but hows this for a temporary solution, add a new seacock on top of the seized open seacock. All I need do is remove elbow and hose, add new seacock and replace elbow, hose. The position of the top end seacock is 100mm above sea level. The worries I have is doing nothing, as when sailing on port tack my bilges will fill with sea water coming up through toilet pan.
rgds Ray