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Septic System Maintenance - Why Does a Septic Tank Need Cleaning? SepticAPedia ©

Enter your search terms Submit search form   Search This Website - InspectAPedia.com Information Provided Here Why Pump or Clean the Septic Tank? Effect of Septic Tank Pumping on System Life Here we explain why a septic tank needs to be pumped regularly, how septic tanks are cleaned, how much it costs to pump a septic tank, how to inspect and clean septic tanks safely, what is septic tank effluent retention time, how to measure septic tank scum and sludge levels, and other septic tank maintenance advice for homeowners. How often should septic tanks be pumped? Why should septic tanks be pumped out? What causes septic field failures? Understanding the proper procedures for septic tank care, septic tank cleaning frequency, and other septic tank maintenance chores, will permit the owner of a home with an onsite septic system to maximize the life of the system and to assure that it is working properly. Also see Septic Tank Pumping Procedure Detailed step by step photo-illustrated guide to find, pump and clean a septic tank. © 2008-1978 Daniel Friedman, All Rights Reserved. Citation of this article by reference to this website and brief quotation for the sole purpose of review are permitted. Use of this information at other websites, in books or pamphlets for sale is reserved to the author. Technical reviewers are invited and are listed at "References." © Copyright 2008 Daniel Friedman, All Rights Reserved. Information Accuracy & Bias Pledge is at below-left. Use the links at page left to navigate this document or to go to Other Website Topics. Green links at left show where you are in our document & website. Our site offers impartial, unbiased advice without conflicts of interest. We will block advertisements which we discover or readers inform us are associated with bad business practices, false-advertising, or junk science. Our contact info is at inspect-ny.com/appointment.htm.

WHY DOES A TANK NEED PUMPING? A Basic Explanation of What Happens in a Septic Tank

The most common domestic wastewater treatment system used in rural areas is the septic tank-soil absorption system. The septic tank removes settleable and floatable solids from the waste water. The soil absorption field then filters and treats the clarified septic tank effluent and distributes it through the soil. Removing the solids from the wastewater protects the soil absorption system from clogging and failure. In addition to removing solids, the septic tank also promotes biological digestion of a portion of the solids and stores the remaining undigested portion.

The first stage of the treatment system, the septic tank, removes solids by holding wastewater in the tank. This allows the heavier solids to settle as sludge and the lighter particles to form scum at the top. To accomplish this, wastewater should be held in the tank for at least 24 hours. Up to 50 percent of the solids retained in the tank decompose; the remainder accumulate in the tank. Biological and chemical additives are not needed to aid or accelerate decomposition. The small, collapsing, and totally impacted septic tank shown here was ignored by the property owner for years, leading to total failure of the system.

This figure shows a tank in cross-section. You will see that the liquid septic effluent volume has as available space the area between the underside of the floating scum layer at the top of the septic tank and the upper side of the settled sludge layer on the tank bottom.

As a septic system is used, sludge continues to accumulate in the bottom of the septic tank. Properly designed tanks have enough space for up to three years safe accumulation of sludge, but the actual time you can allow between septic tank pumpouts depends on tank size and level of usage - see TANK PUMPING SCHEDULE for a table relating septic tank size and usage to pumping frequency.

When the sludge level increases beyond the maximum design point, sewage has less time to settle out as scum or sludge before leaving the tank and more suspended sewage solids will flow out of the septic tank into the absorption area or drainfield. If too much sludge accumulates, no settling occurs before the sewage flows to the soil absorption field. Infiltration of sludge into the soil absorption field will shorten the drainfield life and thus cause system failure by clogging the absorbing soils around the field. To prevent this, the septic tank must be pumped on the proper schedule. The material pumped out of the septic tank is known as septage, raw sewage, or blackwater.

Technical Reviewers

Particular thanks are due to experts and also consumers who read these articles and suggest corrections, changes, and additions to the material. Content suggestions, technical corrections and content critique are invited for any of the content at our website.

• Mark Cramer Inspection Services Mark Cramer, Tampa Florida, Mr. Cramer is a past president of ASHI, the American Society of Home Inspectors and is a Florida home inspector and home inspection educator. (727) 595-4211 mark@BestTampaInspector.com 11/06
• Arlene Puentes, a licensed home inspector, educator, and building failures researcher in Kingston, NY. 11/29/06
• Daniel Friedman - principal author
• Technical reviewers are invited to comment or ask questions - contact us

The Septic Systems Online Book - Where Are We?

More expert information on this topic

More Information on Septic System Diagnosis, Maintenance, & Repair

• The Septic System Information Website home page for this topic
• Septic Systems Inspection, Testing, & Maintenance- online textbook. Detailed how to inspect, maintain, repair information


• The Home Buyer's Guide to Septic Systems
• SEPTIC TANK PUMPING SCHEDULE When, Why, How to pump the septic tank
• Septic Tank Pumping Procedure step by step photo guideline of how to pump and clean a septic tank - septic tank care
• Tank Location - How to Find the Septic Tank, how deep will the cover be, how to document its location
• Home & Outdoor Living Water Requirements
• Septic Tank Capacity vs Usage in Daily Gallons of Wastewater Flow, calculating required septic tank size, calculating septic tank volume from size measurements
• Septic System Design Basics: Choosing Septic Tank Size, Absorption System Size
• Table of Required Septic & Well Clearances: Distances Between Septic System & Wells, Streams, Trees, etc.
• Ten Steps to Keeping a Septic System Working, suggestions from the U.S. EPA, edits and additions by DJF


Pennsylvania State Fact Sheets relating to domestic wastewater treatment systems include

• Pennsylvania State Wastewater Treatment Fact Sheet SW-161, Septic System Failure: Diagnosis and Treatment
• Pennsylvania State Wastewater Treatment Fact Sheet SW-162, The Soil Media and the Percolation Test
• Pennsylvania State Wastewater Treatment Fact Sheet SW-l64, Mound Systems for Wastewater Treatment
• Pennsylvania State Wastewater Treatment Fact Sheet SW-165, Septic Tank-Soil Absorption Systems
• Document Sources used for this web page include but are not limited to: Agricultural Fact Sheet #SW-161 "Septic Tank Pumping," by Paul D. Robillard and Kelli S. Martin. Penn State College of Agriculture - Cooperative Extension, edited and annotated by Dan Friedman (Thanks: to Bob Mackey for proofreading the original source material.)

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