Overall Reliability Properly constructed and installed septic tanks serving greywater systems can have service lives in excess of 20 years and be considered highly reliable. Holding tanks are highly reliable if sufficient attention is given to pumping the tank as needed. Septic tanks should be pumped at an average frequency of 2 to 5 years, in order to prevent too much sludge and solids build-up. The pumping frequency for septic tanks receiving greywater should be less than for those receiving combined wastes. A thorough site evaluation must be conducted in order to determine the appropriate level of pretreatment prior to final onsite subsurface disposal of the greywater portion of the wastestream.
Septic tanks can provide for only primary levels of treatment.
Potential environmental impacts associated with tank truck collection of wastewater include holding tank overflows or leaks, or wastewater spillage during either pumping or transport to the wastewater treatment facility. Transport of holding tank wastewater increases loads and wear for public roads, highways and bridges. Energy Consumption Septic tanks do not require power consumption. Wastewater drains by gravity from the house to the tank. Energy is consumed by the tank truck while pumping and transport the wastewater to the wastewater treatment facility.