The House Detective by Barry Stone, Certified Home Inspector
Dear Barry: We received a letter from the company that pumped our septic tank when we bought our home last year. They recommended that a household of two people should pump the septic tank every 1 ½ to 2 years. They also recommended a septic additive that they sell for $30 per gallon. It’s supposed to break up the solids in the tank, and they claim it’s better than the kind you buy at the hardware store. According to my neighbor, the tank should be pumped every five years. What’s the best advice for maintaining our septic system? Larry
Dear Larry: The septic company’s maintenance advice is better for them than for you. It improves their bank balance and does nothing to benefit your septic system.
On average, septic tanks should be pumped every 3 to 5 years, depending on the size of the tank, the number of family members contributing waste to the system, and the kinds of solids that go down the drain. Most solids that enter the system are decomposed by the bacteria in the tank. Eventually, non-organic junk, such as sand and bits of plastic, accumulate on the bottom of the tank, while a layer of floating grease and scum accumulates on top. These solids reduce the efficiency of the system and make pumping necessary.
Larger septic tanks need pumping less frequently than smaller ones because they have a larger capacity for junk and scum. Likewise, the fewer people who use a system, the less often pumping will be needed. For example, a 1,500-gallon system being used by a family of four might need pumping every five years, while a smaller tank would require pumping twice as often. After the kids have grown and flown, a 1,500-gallon used by empty-nest parents might only need pumping every 10 years.
Garbage disposals can also affect the frequency of septic pumping because they increase the volume of solids in the system. And undigested solids, such as those from a garbage disposal, take longer to decompose.
Additives to septic systems are widely recommended, but their benefits are doubtful. Controlled studies have not shown them to improve the performance of septic systems in any significant way. Added enzymes and bacteria cannot break down non-organic sediment. And added bacteria must compete with the bacteria already in the tank. In most cases, the established bacteria simply eat the added ones.
So don’t let contractors sell you on needless septic maintenance. Their advice will simply add wasted money to the solid waste already in your system.