What is the weight of an empty tandem dump truck?

20,000 - 25,000 lbs. tare would be a good estimate. The weight's going to vary by a number of factors, to include wheelbase, powerplant, what the bed is made out of (steel vs. aluminum), etc. And the model of truck will affect it, as well. E.g., a Mack RD series is going to be much lighter than a Western Star 4964 series truck.