A dousing system is generally one in which the 
septic tank waste is collected into a tank and the
contents of this tank are pumped periodically into the drainfield. This allows the drainfield to receive a constant volume per douse. The drainfield can be either a gravity fed system or a pressure system. 

The above ground system is generally used when the ground cannot accept the flow required for the drainfield. A dousing system would not help in these circumstances to reduce costs.