Pat!
we cleaned our tank by opening the inspection hatch and pumped out the rest with a hand pump same as on our outboard tank. We used a fuel hose with inner diameter the same as the outer diameter on the hose with the hand pump to make it reach down the tank. I had a length of Aluminium tube that fitted well into the fuel hose so it became very easy to position the end at the lowest point I got out most of the fuel less than half a liter left then I toke a broom with a cloth and cleaned the tank, looked as new after that. total time a few hours.
Paul on SY Kerpa SM#259