In general it is recommended that septic tanks should be pumped out every 3-5 years. I live within the Chesapeake Bay watershed in a resource protected area that requires a septic tank pump out at least every five years. Many localities do not have set requirements. However, just because no one requires you to pump out your septic tank, does not mean that the tank does not need to be pumped out. How often you need to pump your septic tank depends primarily on the size of your tank, the number of people in the household contributing to the volume of your wastewater, the volume of solids in your wastewater and whether you use a garbage disposal or have a water treatment system. According to the EPA, the use of a kitchen garbage disposal will increase the amount of solids in the holding tank by as much as 50%. It is the amount of soils in the tank that ultimately will cause most septic problems. The chart above is from the Montana Extension Office and gives a general rule of thumb for frequency in pumping a septic tank to avoid failure. This chart assumes that the system is properly used and does not have a garbage disposal in the household nor a reverse osmosis water treatment system discharging into the tank.
According to the U.S. Census Bureau, New England and southeast have the highest proportion of homes served by septic systems. Having grown up in New England with an old septic system and now living in the southeast, the rules of care to minimize the need for pumping the tank and maximizing the life of a septic system are second nature to me. Only human waste and a limited amount of toilet paper are to be flushed done the toilet. A toilet and septic system is not a trash can. Don’t put dental floss, feminine hygiene products, condoms, diapers, wipes, cotton swabs, cigarette butts, coffee grounds, cat litter, paper towels, latex paint, pesticides, or other hazardous chemicals into your system. Never do more than two loads of laundry a day. Cooking grease is poured into a can under the sink, and all plates are scraped into the trash or compost. Commercial septic tank additives add bacteria to the system and in some instances may assist in the breakdown of fecal waste, but do nothing for the breakdown of vegetable matter, and trash that you have put down the drain. The EPA believes that the commercial septic tank additives have little if any effect on the need for pumping the tank and believe in most instances the bacteria already present in the tank eat the added bacteria.
A typical septic system has four main components: a pipe from the home, a septic tank, a leach field (alternative systems might have drip fields, sand mounds or peat tanks where a leach field is not possible or has failed), and the soil. Microbes in the soil digest or remove most contaminants from wastewater before it eventually reaches groundwater. The rest of the system is designed to remove most of the contamination so that the soil is not overwhelmed and can “polish” the water before it is returned to groundwater. Many systems also have pumps to move the liquids from the home to the septic tank or from the septic tank to the drain field. There are also Alternative systems that have additional components such as; float switches, pumps, and other electrical or mechanical components including additional treatment tanks. However, the main functioning components are the septic tank and the leach field.
The septic tank is a buried, watertight container typically made of concrete, fiberglass, or polyethylene. It holds the wastewater long enough to allow solids to settle out (forming sludge) and oil and grease to float to the surface (as scum). It also allows partial decomposition of the solid fecal materials. Anaerobic (without oxygen) digestion takes place with the aid of bacteria that came from human digestive tracks and most of the fecal solids are converted to carbon dioxide, water and other byproducts. The process is not completely efficient and fecal solids and other materials that find their way into the septic tank will accumulate over time. Compartments and a T-shaped outlet in the septic tank are intended to prevent the solid sludge buildup and floating scum (grease, oil, dead skin cells, etc.) from leaving the tank and traveling into the leach field area. Some newer systems have screens and filters to keep solids from entering the leach field. These filters and screens become clogged and need to be cleaned out regularly. Clogging of the filters can cause the system to backup.
The basic design of a septic tank will only work if the sludge is not too thick on the bottom and the grease and scum is not too thick on top, and if the flow to the tank is not excessive. If there is too much waste on the bottom of the tank or too much water flowing to the tank, there will not be enough time for the solids and liquids to settle out before the tank starts releasing waste. If there is too much water flow for the void area in the tank, water containing large amounts of solids and fecal waste and grease will be released to the drain field. The most likely time for your septic system to back up is when water use is highest-when you have a lot of guests at your home using the bathrooms, running the dishwasher and doing laundry, in short, the holidays. A backed up septic system is usually caused by a blockage between septic tank and leach field causing the tank level to rise and back up. If the liquid level in the septic tank is found to be above normal, either: the tank outlet is plugged or in newer systems this can be caused by a clogged filter, the line to the absorption field is obstructed, or the absorption field is clogged and pretty much ruined. An absorption field is destroyed slowly over time. If the absorption field is clogged there will probably be evidence of seepage or general wetness in the absorption area. In dry summer days stripes of green grass over the absorption field may be an indication of a failing system.
A plugged tank outlet can be caused by several things. In septic tanks which have been used for many years, the outlet baffle or “T” sometimes disintegrates or collapses. This allows scum and sludge solids to overflow and plug the outlet or the line to the absorption field. A tank with too much scum and solids that has a large flow of water will also cause solids and scum to overflow the tank. In appropriate stuff like hair, dental floss, feminine hygiene products, condoms, diapers, cotton swabs, cigarette butts, coffee grounds, cat litter, paper towels can be stirred up by too much water use and pushed out of the tank and cause a blockage in the outlet line. Newer septic tanks have filters and screens that can become clogged. Tree roots getting into pipe joints or the collapse of a pipe section can also block the line.
To prevent problems, you can be the household septic police and make sure that only reasonable amounts of grey water, human waste and a limited amount of TP are put into your septic system at all times. This is one way you will avoid that classic holiday disaster of the septic system backed up into the basement, but your family may think of you as a crazy control freak. There is another approach. I clean my filters and pump my septic tank just before the holiday season every year. I do not have to remember what year it is, I do not have to make sure every guest treats my septic system like the elegant, natural system that it is. By pumping the tank each year, I prevent excess sludge (solid material) from building up inside the septic tank, and flowing into the absorption field, and clogging it beyond repair. In the long run I extend the life of my septic system, protect the groundwater and my well, avoid holiday disasters and I can be a slightly more relaxed septic cop. Be aware though that the plumbing system can also get clogged. Waste lines in the house (especially from basement bathrooms) can become clogged with too much paper and not enough water or disposable cleaning cloths that should not be flushed. If this happens you will have to snake the waste line. Toddlers love to flush things down the toilet.
