I use a copper pipe, about 3/4 inch I think (I'm not on the boat now), but it fits quite neatly in the pipe and through the seacock with a few mm to spare. I had a complete blockage and shoved this pipe down and it clerared it immediately. My only concern was to pull it back up and not get it stuck, which fortunately never happened. I'd be interested in any other opinions on this.
Ya Fohi - Amel 54 #98