I have always been more concerned with the black tanks.
My neighbor had one fail from cracks in the tank bottom.
When the tank is full the bottom is like an old oil can but the material the tank is made from does not do well when flexed.
The material the fresh water tank is made from is much more resilient.
I always empty my black tanks ASAP. If I am in back country I travel much slower and carefully until I can dump the black tanks.