Through the small cut out for the tank gauge we were able to see the heavy polluted fuel. There was no way to clean it via the small opening so Brend decides to make a bigger hole. First he had to pump out the old diesel. Then he drilled some holes in the pattern of the new inspection hatch. Eventually he used two jigsaw blades and water as coolant to connect the drill holes. The entire tank was cleaned and rinsed on the inside and made dry. The new inspection hatch was installed and closed firmly. At last he topped up the tank and made sure that there was no leakage. Everything was back to normal and the bed, which is on top op the tank, could be restored just as if nothing had happened.