Septic tanks are sized based on retention time, which is proportional to the volume in the tank. Increased volume results in more retention time. As solids accumulate in the tank, both volume and retention time decrease. More retention time allows slower movement of water through the tank, enabling more solids to settle out of the wastewater. When solids build up, the volume decreases, reducing retention time. Consequently, as solids fill the tank, water carries more solids and clogs the drainfield or makes other system components less effective. Aerobic treatment units, recirculating media filters and even simple effluent pumps work better and last longer when suspended solids and grease are reduced. Pumping the tank regularly removes these solids, preventing system failure. This process also increases tank volume, slows the low through the tank, improving the settling of solids.
Research at Penn State has shown that on-site systems benefit from periods after pumping when they do not receive effluent. In a 2023 article, Professor Albert Jarrett recommends pumping before vacations for extra days without effluent. Jarrett’s article advises homeowners to routinely pump their septic tanks every two or three years to enhance their wastewater disposal system’s effectiveness. Pumping it a week before vacation and using water sparingly prior to leaving, could mean the entire system has a 2 – 3 week vacation. Plus, there will be plenty of laundry and catch-up cleaning when you get back home that stresses the system, so there’s an additional benefit to letting it rest while you’re away.
Measure Solids vs Pumping
If a tank is measured at 20% solids this year, it may not require pumping since some regulations and most recommendations state that pumping is necessary only when solids reach one-third of the tank’s capacity. Therefore, at year three in the cycle, the tank wouldn’t be pumped. However, with 20% solids, the tank volume and retention time are reduced, leading to more solids escaping the tank and potentially causing system issues.
If the homeowner chooses not to pump at year three, solids levels in subsequent years—four, five, and six would remain unchecked unless the county or the pumper has a yearly reminder notification system until the volume reaches 30%. inspection at year six. Also, without pumping, there is no visual assessment of the tank’s condition, which can reveal issues like root intrusion, broken Tees, structural cracks or water intrusion.
Regular pumping is crucial for the longevity of septic systems, as it prevents solids from clogging soil pores. During system backups, professionals typically address issues, not those who only measure solids. Routine pumping every three years is common sense and essential for maintaining system health. If the system is not pumped but only measured, it should undergo annual inspections until the next pumping.