I am with the group that carries water. The fresh tank is typically filled to 2/3rds or more, the black and gray have about 5 gallons to keep them from drying out. Twice I have hooked up to really foul tasting CG water.
When I crossed that Cat scales loaded heavy for the road with the TT weighting 6400 lbs; of which 700 lbs was tongue weight, leaving 5700 lbs. on the 7000 lbs rated axles, I realized I would run out of TV cargo capacity long before I overloaded the TT.
Those with bigger TV's might not have such problems but my max cargo is 1411 lbs. half of which is tongue weight.