Drip irrigation uses the same aerobic treatment unit as a surface spray system except for the need to disinfect the wastewater. The wastewater passes through a filter to remove larger particles before reaching the drip tubing, a 1/2" flexible tube with what are called drip emitters spaced every 2 feet buried within 1 foot of the ground surface. Though methods vary typically there is a supply line coming from the pump that tee's off into each run of drip line with the drip line running out and looping back into a return line that feeds back into the pump tank of the aerobic unit. A gate valve and pressure gauge is used to set the pressure within the drip bed, the drip emitters will only operate if there is pressure and this ensures wastewater, dirt, ect. does not enter into the drip line from the outside. The pump is typically controlled by a timer that doses the wastewater out into the disposal field at set intervals so as to avoid over saturation of the ground while ensuring wastewater is disposed of quickly enough to meet the needs of the household. These systems are primarily used for sites that do not have enough land area for a spray disposal field or when a homeowner prefers a subsurface disposal method for their wastewater. The size of the disposal field required is determine by size of home and clay content of soil.