A driver is preparing to load a dense liquid such as a strong acid into a cargo tank. Why might the driver only partially fill the tank, even though it has more physical capacity available?

AAMVA CDL Manual, Section 8.2.7, p.8-8-2

Dense liquids like concentrated acids weigh far more per gallon than fuel, so filling a tank to its physical limit can put a rig well over its legal gross weight. A driver who understands this avoids costly overweight citations and the handling problems that come with an improperly loaded tank.