Abstract: A trailer provides a slurry hauling tank having an auger mounted for swinging movement inside the tank. A rotary hydraulic motor inside the tank drives the auger and is powered by fluid delivered through a rotary fitting extending through the tank wall. Relatively stiff stainless steel conduit connects the rotary fitting to the auger motor. The auger is oscillated through an arc while the trailer is being loaded, towed toward a disposal site and during unloading by a hydraulic motor on the outside of the tank. A hydraulic circuit alternately drives the motor in one direction and then in another direction. In one embodiment, the hydraulic circuit reverses by use of a pressure responsive cycling valve. In another embodiment, microswitches are used to reverse the hydraulic motor.