Rural homeowners often wonder how often they should have their septic tank pumped. Unfortunately, we can’t give them a number or formula because it depends. The pumping frequency required will depend on the size of the tank and how many solids go into it. A larger tank will have a longer time interval between pumpings than a smaller tank. More importantly, the tank will have a longer interval between pumpings if the amount of solids going into the system is minimized.
Heavy solids fall to the bottom of the tank where they form a layer of sludge. Lighter solids float to the top of the tank where they form a layer of scum. The tank must be pumped before the sludge and scum layers become too thick, reducing the effectiveness of the system. When sludge and scum build up, the effective tank volume is reduced. Wastewater moves through the tank more rapidly and receives less treatment. In addition, solids can be carried to the drainfield, causing it to clog.
We recommend the following to determine the pumping frequency for your tank. Have the tank pumped by a certified Nebraska pumper. Then, have a certified pumper or installer check the tank annually to measure the sludge and scum depths. Nebraska Department of Environmental Quality regulations (Title 124) define the maximum volume of sludge and scum allowed before pumping is required. Your certified pumper or installer will be familiar with the regulations, which state that a tank must be pumped when the bottom of the scum layer is within 3 inches of the bottom of the outlet baffle, the top of the scum layer is within 1 inch of the top of the outlet baffle, or the top of the sludge layer is within 12 inches of the bottom of the outlet baffle. They also will know how to measure the sludge and scum using a specifically designed measuring tool or a two-stick method. With this information, your certified professional will be able to determine if the volume of sludge and scum in your tank is approaching the point at which pumping is required.
Have the tank pumped when the sludge and scum depths require it. How many years passed since the initial pumping? This will be the pumping interval for your tank as long as your wastewater generation remains the same. Repeat the process or adjust pumping frequency if wastewater generation changes.
You can do some things to minimize solids entering your tank. First, do not use a garbage disposal, or use one sparingly. Studies have shown tanks need to be pumped twice as often when a garbage disposal is used. Other tips include:
Do not flush cigarettes, diapers, feminine hygiene products, paper toweling, facial tissue, or “wipes.” They may not break down readily and will contribute to the scum or sludge layers. Dispose of these items with other solid waste.
Do not put grease or oils down the drain. Grease and oils from cooking, frying, and skin lotions increase the scum layer in the septic tank.
Use liquid detergents instead of powdered detergents. Powdered detergents have “fillers” in them that add to the sludge layer.
Use toilet tissue that breaks down rapidly. Test by placing a tissue sample in a jar of water, covering the jar opening, and shaking vigorously. The toilet paper should fall apart rapidly when the jar is shaken.
Install a filter on the washing machine water discharge line to trap lint. Clean according to manufacturer’s directions.
Install an effluent filter at the outlet of the septic tank to help prevent solids from flowing into the drainfield. Have it cleaned according to manufacturer’s directions.