Final answer:
A portable tank mounted on a truck or trailer requires a tanker endorsement on a commercial driver's license if it holds more than 119 gallons.
Step-by-step explanation:
A portable tank mounted on a truck or trailer requires a tanker endorsement on a commercial driver's license if it holds more than 119 gallons.
The requirement for a tanker endorsement is based on the size of the tank, not the weight of the tank or the vehicle it is mounted on.
Therefore, any portable tank with a capacity of 120 gallons or more would require a tanker endorsement on a commercial driver's license.