How Does a Septic Tank Work?

How Does a Septic Tank Work?

Sewage from all plumbing fixtures drains into the septic tank, where heavy solids settle to the bottom, where bacterial action produces digested sludge and gases. The lighter solids, such as grease, oils and fats, rise to the top to form a scum layer. Solids that are not decomposed remain in the septic tank.

How Much Does a New Septic Tank Replacement Cost?

It is hard to estimate because most septic tank systems are dependent on the specific home. However, prices for the tank itself can generally range from $600 - $2,000, depending on the size of the tank and the material.

However, don't underestimate the cost of installation, which can also range between $3,000 - $20,000, depending on if the leach field needs to be replaced as well. When it is all said and done, a conservative estimate for a replacement tank and installation might be around $6,000-$8,000, or more.

Parts of a Septic Tank System

The most common type of septic system has four main parts:

  1. An exit pipe that carries wastewater from the home to the septic tank and vents noxious gases up and out of the house
  2. A buried, watertight septic tank made of concrete, fiberglass, or polyethylene, usually installed about 6 feet from a home
  3. The drainfield, which consists of one or more distributor boxes and a network of pipes buried in relatively shallow trenches that are usually packed with gravel or other filler
  4. Soil, full of bacteria that digest most contaminants before wastewater reaches groundwater.

Do Septic Tanks Have to Be Emptied?

It is important that you empty your septic tank. If the tank is not cleaned, the waste inside will start to fill the first chamber, leaving less and less space for solids and liquids to settle and separate.

The solids may also start to thicken, becoming encrusted on the sides of the tank and the dip pipes. If any significant movement takes place in the tank when this happens, it is possible for the crust to become so thick that the dip pipes will break. This will allow fats and floating solids to pass straight through to the soakaway, without being filtered.

How to Find Out If Your Septic Tank Is Full

First you’ll need to locate and carefully remove the septic tank lid. Use extreme caution so that the heavy lid does not crack or break, and never leave the open tank unattended! The tank contains 4-5 feet of water underground and can be dangerous if a human or a pet falls in.

Then the next step is to take a look at the scum trap at the top to assess how thick the scum layer is. In general, you want to pump your septic tank when the scum level reaches 6 inches thick.

The second step is to measure the level of sludge at the bottom of the tank, which is a little more involved. While you can purchase a specific sludge level measuring stick, you can also make a homemade version.

Simply take a seven foot strong stick or two by four and adhere a 18-24 inch velcro strip along the stick, starting at one end of the stick. The velcro end will be the end that goes into the tank.

Keeping your measuring stick upright, lower the velcro end of the stick gently straight down into the septic tank, even through the thick sludge at the bottom, until you feel the stick hit the bottom of the tank. Then remove the measuring stick straight up and check the velcro strip.

Because the dark thick sludge will cling to the velcro, and you’ll be able to measure for yourself approximately how many inches of sludge are at the bottom based on the inches of sludge along the velcro strip on your stick. We recommend that the septic tank be pumped as soon as it reaches 1 foot (12 inches) of sludge.

What Time of Year Is Best to Empty Septic Tank?

The best times to pump your septic tank are spring and summer. A tank that is near capacity should be pumped during the spring to avoid flooding from heavy spring rain showers. It's a good idea to pump your tank in the warmer months in preparation for high usage and to make maintenance easier for your technician.