Septic Tanks Should Be Cleaned Before Winter

NEWS for North Dakotans
Agriculture Communication, North Dakota State University
7 Morrill Hall, Fargo, ND 58105-5665

October 15, 1998

Septic Tanks Should Be Cleaned Before Winter

Fall is a good time to have your septic tank cleaned to make sure you don't have problems flushing the toilet during the coming winter and early spring, according to a North Dakota State University agricultural engineer.

"Periodic cleaning of the septic tank is required maintenance for an individual home sewage system," says Tom Scherer of the NDSU Extension Service. "Frozen and saturated soil conditions slow the flow of effluent out of the tank, so getting the tank into top condition before winter is a good idea."

The septic tank's main purpose is to separate the solids from the liquids, allow bacteria to break down the solids and store for removal the solids that don't break down. The solids that stay in the tank, sludge, is mainly composed of dirt (from washing clothes) and products of decomposition that are heavier than water.

As sewage is broken down in the septic tank, some solids settle to the bottom, and others float to the top, Scherer explains. This separation produces three distinct layers within the tank. The top layer is a scum composed of cooking fats and oils, soap byproducts and products of decomposition which are lighter than water. Between the sludge and the scum layer is the liquid layer. The liquid layer discharges to the drainfield while the solids are retained in the septic tank.

"When the sludge that can't be broken down by bacterial action accumulates to a certain depth in the tank, it must be removed," Scherer says. "Without removal, it will move with the water to the drainfield. Those solids can plug the field which will cause the effluent to back up into the house and/or rise to the ground surface. Fixing either problem, especially in the winter, can be messy and costly."

Most properly sized septic tanks need cleaning about every three years. However, the actual time will depend on the quantity of solids entering the tank. If you have a garbage disposal in the kitchen sink, the tank should be cleaned every one or two years, Scherer says.

If you are unsure whether your septic tank needs to be cleaned, the sludge layer can be measured. To measure the sludge layer in the bottom of the tank, secure 3 feet of white terry cloth or toweling, rough side out, around a wooden or metal pole and push to the bottom of the tank. Turn slowly two or three revolutions, let sit for a minute then slowly withdraw. Sludge thickness can be measured where black particles cling to the rough cloth. If the sludge is more than 12 inches thick, have the tank cleaned.

Scherer discourages the use of commercial products that claim to renew septic tanks through the use of enzymes and special bacteria. Those components mainly affect the scum layer, breaking it into smaller pieces which can get carried into the drainfield and contribute to plugging.

"Have your septic tank pumped by a licensed contractor," Scherer says. "Cleaning a tank is more than just pumping out the liquid. The scum and sludge layers must be broken up by pumping and back-flushing the liquid into the tank several times. The mixed contents can then be pumped from the septic tank and disposed of by an approved method."

The only sure way to effectively clean a septic tank is through the manhole, not through the inspection ports (4- to 8-inch diameter pipes that come to the surface over the inlet or outlet baffles). If the licensed contractor cleans the tank through the inspection ports, he may break or dislodge the baffles, Scherer says. Breaking the baffles can prevent free movement of effluent into and out of the septic tank. When the septic tank manhole is open, have the contractor check the condition, length, and submergence of the inlet and outlet baffles. If they are corroded or broken, have the contractor replace them.

"For safety sake, never allow anyone to go down into a septic tank unless a continuous fresh air supply is pumped into the tank and a strong rope is tied around their chest," Scherer says. The person outside the tank must have enough strength to pull the person out of the tank. Fatalities have occurred during septic tank maintenance and repair because of the buildup of toxic gases.

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Source: Tom Scherer (701) 231-7239

Editor: Tom Jirik (701) 231-9629

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