Our engine was producing some white smoke which can be due to water getting burned with the fuel. We thought it was time to check how the diesel tank looks inside and possibly change the fuel to see if it solves the issue.
The tank has no inspection hatch, so it had to be done through the fuel gauge opening. Once opened, I could clearly see that the tank needs to be cleaned and the fuel is full of water. There were growth flowing in the fuel too which could clog the filters any time. Unfortunately the fuel gauge opening is very small, so my hand won't fit in, I had to find some other way.
Then I picked up a flexible "grabber" which can be used to grab stuff from difficult places and used it with tons of paper towels to clean the tank.
We changed both fuel filters and filled the tank with fresh fuel. While at it, we also replaced all fuel hoses (6 meters of 8mm Lloyds approved marine grade hose) from the tank to the engine as the old ones were showing signs of wear.
The extensive white smoke issue is now gone and the engine runs much better.