bid_time wrote:
In the world of physics in order to answer the question you would have to know the center of gravity of the trailer vs. the center of the axle(s) vs. the center of gravity of the tank vs. how much water is in the tank.---
I don't know about your world -- but, in my world of physics, the answer to the original question does not depend on either the location of the center of gravity of the trailer or how much water is in the tank.
The question already has been answered correctly --
If the tank is ahead of the axles' center, adding water will increase tongue weight.
If the tank is behind the axles' center, adding water will decrease tongue weight.
If the tank is directly above the axles' center (approximately the OP's configuration), adding water will not change tongue weight.
Ron