Just because the sight glasses are full of red liquid doesn't mean it is good usable diesel fuel. Look for a bottom drain valve on each of the tanks and very slowly take a sample in a clear quart jar from each tank.
If you see any black stuff come out it is allege, and the tanks will have to be washed down and the fuel polished to 2-microns. The last thing you want is to go to sea with dirty fuel and/or dirty tanks.
Welcome to the forum and don't let all of us old guys scare you away.