This job looked like a pain in the ass for little gain (if the fuel was OK).
I should mention at this point that the "fuel gauge" was a rudimentary piece of wood that you needed to insert through the deck filler. If you look closely at the photo below, you can see the "calibration" marks.
I did not fancy using this in a heaving seaway; a more modern sender and gauge were required. This necessitated the removal of the tank from the wet locker behind the heads. Pain in the ass it was, as I tried with great difficulty to get my 6'3" frame through the locker door to unscrew the endless jubilee clamps on the filler & breather pipes (one handed!).
Eventually I got the tank out and as I emptied the fuel it quickly turned from clear to a murky mix as I got near the end. Poking a flash-light down the filler hose showed this sludge, visible in the photo:
|Sludge in fuel tank|
Big Al was right (again). 30 years of sludge in the bottom of the tank. Apparantly bacteria and certain types of fungi thrive in the marine/diesel environment (I can't imagine why) and the sludge visible is the result. Fortunately the filler hole is 2" in diameter which enables me to get a brush on the end of a stick, into the tank to clean it out.