2005 Mack automotive transmission with a 2006 M-1500 Surface to Surface mixing system with two 750 gallon tanks. There is around 600k miles on truck just had it DOT inspected. The mixing system has a gasoline engine.The M-1500 was designed and manufactured as a dual tank system that allows the HDD Contractor two methods of mixing there Bentonite mud requirements. This system allows the operator to mix 750 gallons of full yield mud in less than eight (8) minutes, while holding 750 gallons of water reserve in the second tank for the next mix, or mix 1500 gallons of full yield mud in less than sixteen (16) minutes, in one large batch. The operator controls the two methods of mixing by changing the direction of flows through the piping connections using the manual operated full flow valves. The vacuum port located in the mixing tee has the ability to draw water from the second tank when being used as a reservoir and the drill fluid can then be sent to the drilling rig with-out the use of a second pump.