See i am not sure if my ans would be correct because it is too simple.
u had said earlier the vessel is sealed, so i take it as a closed vessel which is transparent.
first mark the water level. then invert it. if the water level is greater than the marked level, then it means the water in the vessel is more than the volume of vessel. if water level and the marked r same then the volume is less and if water level is lower the volume is less.