Here's the problem with the dust control trucks. The glue (Gorilla Snot) bonds to the tank. The water tanks usually have 1 coat of primer and 1 color coat, without a clearcoat. The dust control solution used (there are several differant brand, the company I do the trucks for uses Gorilla Snot) is basically a watered down version of Elmers glue. Without a clearcoat on the exterior of the tank, the glue bonds to the paint, making it all but impossible to remove without lifting the paint and primer coats.
I have found the solution is to completely strip the tank, have them repainted, including several coats of clear coat. Gorilla Snot makes a product that must be applied at least once a day to the exterior of the tank to prevent bonding. Then the operator of the truck needs to completely hose down the truck at the end of shift.
The Gorilla Snot play hell on the water pump and lines also, and the interior of the tanks can become ridiculously full of dried snot. I know the company who's fleet I have the contract for uses gasoline inside the tank and to clear the lines and the pump.
Hope this information helps. I have made plenty of $$$ from this company maintaining their fleet. If the company you are servicing is using a product different that Gorilla Snot, then I would contact the distributor directly for their support and suggestions.