the pipe with the cinder block is the one that is probably clogged. This is a rebuild from Captain Petes boat....He installed a pipe in the forward area as well to drain the cuddy but my 87 cuddy doesnt have that as I can see the bottom of the boat through the drain hole in the cuddy floor and the fish box which is in front of the fuel tank.. Just the one that goes under the fuel tank.
you're looking for something like this:
