A septic truck is a style of vacuum truck used exclusively for emptying septic systems. The tank is on the rear of the truck and features a pump that creates negative air pressure. This negative air pressure is what pulls the septage into the tank. Tanks range in size up to 1,940 cubic feet capacity.
Although there are two ways to mount the pump, there is one way that is best. A pump mounted on the truck and uses the truck motor is the efficient method. You can mount the pump on an independent motor on the trailer. That method is more difficult and causes more work for the driver. The suction hoses are two to four inches in diameter and the length is up to 160 feet.
To unload the tank, the driver uses gravity. You can try to pressurize the tank, but it deteriorates the equipment. Letting nature take its course means it takes 10 minutes per 4,000 liters to empty the tank.