as you may know the tank has no drain plug [ thanks nissan ] so it would be quite hard to clean out the tank unless you remove the inlet hose and use a length of rubber hose with a pump attached, you would have to add about 4 litres of fuel to the empty tank then rock the car so any water etc will mix in the fuel then pump drain out quickly, might have to do this atleast 3 times . add a lead sinker weight to the rubber hose that will go into tank so it stays on the bottom to pick up water etc. my son did add petrol to his diesel tank and this was the way he removed all water from the tank .