If your Nordic Tug has sight gauges on the water tank and the fuel tanks it is easy to read the tank levels. The drawback is that we use the tank rooms for storage and a stored item could get loose and crash into the sight gauge breaking it. You could drop a full tank of diesel fuel into your bilge which would be a real bad day. Close the valves at the top and bottom of the sight gauges except when reading them. That way if the tube breaks a very limited amount of fluid is spilled.