I have inspected about 500 septic systems, and I cannot even count how many times the homeowner has told me, “we’ve never had a problem with it, so we’ve never had it pumped.” That is just like saying, “I’ve never had any trouble with my car, so I’ve never had the oil changed.” Just like you change the oil in your car to help to protect your car, you should have your septic tank pumped in order to protect your septic system. Let’s look at the basics of a septic system.

Septic System Components

A typical anaerobic septic system has two main parts: a tank and lateral lines. The septic tank receives the waste water from the home, including from the commodes, tubs, sinks, etc. The solids will settle to the bottom of the tank where it becomes sludge, the lighter material such as grease and oils will float to the top and becomes part of the scum layer, and the water will form the middle layer in the tank. Septic tanks should be sized according to the size of the home, taking into account, among other things, the number of bathrooms in the home. The tank’s size is important because it will determine the retention time. The retention time is how long the material that flows into the tank will remain in the tank. For example, if a home uses 500 gallons of water per day, and the volume of the septic tank is 1000 gallons, then the retention time will be two days. The minimum retention time that a tank should have is 24 hours. This will give most solids time to settle to the bottom of the tank, and will allow the lighter materials to settle on top of the liquid. This settling is important because it minimizes the amount of sludge and scum that will flow out into the lateral lines; and keeping sludge and scum out of the lateral lines is critical to the efficient operation of a septic system.

The lateral lines are buried about 18 – 24 inches underground and they are what the water flows into once it has flowed out of the tank. There are various kinds of lateral lines such as perforated pipe and panels.   Lateral lines will always have holes of some kind that will allow water to run out of the lateral lines and to flow into the soil where it will then percolate down through the soil, getting purified as it does so.  

Septic System Operation

Let’s look at the basic operation of a septic system. The tank is always full of water with some amount of sludge on the bottom, and scum floating on the top of the water. Let’s assume that someone in the home drains a bathtub or flushes a commode and that a total of ten gallons of water flows through the drain line and into the septic tank. As soon as that ten gallons of water begins to enter the tank, the water level in the tank rises above the level of the outlet line in the tank, so water begins flowing out of the tank. A total of ten gallons of water will flow out of the tank, into the lateral lines, and then into the soil. In the meantime, any solids that came into the tank with the liquid will slowly begin settling towards the bottom of the tank – thus adding to the sludge later. Any oils, greases and soap scum will begin floating up and will eventually become part of the scum layer.

Although many older systems do not have them, all septic tanks should have “T” baffles at the tank’s inlet and outlet. Looking at the diagram, you can see that these baffles prevent water/scum that is at the top of the tank from flowing directly into the outlet line. Without the outlet baffle, scum and any trash floating on the top of the liquid could flow straight out of the tank and into the lateral lines. This would result in the lateral lines quickly becoming clogged. The inlet baffle helps to direct all of the incoming liquid downward. This minimizes mixing action and helps the solids to settle to the bottom of the tank more quickly.

Septic System Maintenance

If you follow a few simple “rules,” your properly-installed septic system should provide many years of trouble-free service. Septic systems do a remarkably efficient job in digesting biological products. The average tank will break down about 50% of the solid waste that enters the tank, with the rest of the solids settling to the bottom of the tank as sludge. Non-biological products will not breakdown, but will remain in the tank indefinitely. Therefore, minimize the amount of non-biological products that go into the tank. The only one that I would even consider allowing into my septic tank would be toilet tissue. Never put any other paper products, plastics, or any other non-biodegradable material into your septic tank.

You should also avoid putting fats, greases or scrap foods into the tank. It is not a good idea to use a garbage disposal if you have a septic system. Do not put bleach or other chemicals into your septic tank as it will kill the bacteria in the tank that is required to break down the solids in the tank. Another, less intuitive thing to not put into the tank is too much water. Water? Yes. Too much water can cause several problems. It can disrupt/dilute the bacteria in the tank that is essential to breaking down solids. It can saturate the soil – affecting its ability to absorb septic tank effluent. Lastly, it will lower the retention time and not give the solids and liquids time to settle out of the liquid.

Now we come back to what I said at the beginning of this article. You MUST have your tank pumped regularly. The leading cause of septic system failure is the failure of the drain field, and one of the leading causes of drainfield failure is sludge and trash from the tank getting into the lateral lines. The rule of thumb is to have your tank pumped every 3 – 5 years. The frequency of pumping will depend on a lot of factors, including how many people are living in the home, the size of the tank, etc. I have inspected tanks that have not been pumped for more than ten years and that still don’t have enough sludge to necessitate pumping. I have also inspected tanks that have been pumped within the last five years and already needed to be pumped again.

In conclusion, take care of your septic system, and it will take care of you. Do not put things in the tank that do not belong in the tank. Pump it regularly. Do not flood your system with excessive water. Following these suggestions should help to keep your septic system functioning well for years.