Save Money by Understanding Your Septic System

Knowing Your Septic System WILL Save You Money

What happens when you flush the toilet? Where does the wastewater go? For those of you not connected a municipal sewer line the solution lies in the septic tank.

A septic tank is just one component of a septic system. A system can be as simple as a septic tank and drain field or include any number of necessary add-ons such as an aeration pretreatment tank, grease trap, baffle, filter, pump or siphon chamber, distribution box or sand mound.

The size of the tank depends on the number of bedrooms in the house not the number of people or plumbing fixtures. The sizes range from 750 gallons on up and there can be 1, 2 or even 3 tanks. Having 2-3 tanks (or a 2 compartment septic tank) increases retention time of the waste material which helps to further reduce the suspended solids that could flow into the drainfield. 

The drain field or sold infiltration system is the area where the liquid from the septic tank soaks into the ground. The micro-organisms in the soil remove the viruses, bacteria and most other contaminants and nutrients typically found in household wastewater. This drainfield area may be 1 or more trenches that are 5 feet wide or less, a rectangular bed or an above grade design like a mound. 1 or more vents or observation tubes are placed in the drainfield area.

When the gray water or effluent has to be lifted uphill into a drainfield, another tank is installed after the septic tank. This tank contains a pump with floating on and off switches to send the wastewater into the drainfield at preset intervals. This pump tank also known as a pump chamber or lift station has a high water alarm float switch connected to an alarm installed inside the building to warn the user when the pump is not working. Since 1980, pump tanks have about 1 one-day use capacity once the pump fails and the alarm sounds. However, most septic systems effluent pumps are maintenance free for many years.

The waste going into the septic tank comes from the bathroom toilets, garbage disposal, laundry tub, washing machine, sinks, dishwashers, bathtubs and showers, water softener, furnace and humidifier. The first 2 components are called blackwater waste. This waste contains most of the solid wastes and a majority of the pathogens and nutrients. The other components are referred to as greywater waste (water from washing and cleaning). All this material going into the septic tank separates over time into three components:

  1. Grease, fat and floating solid materials (scum) which rise to the top of the tank.
  2. Liquid waste - mostly water.
  3. Solid waste and sludge that settles to the bottom of the tank.

The solid waste is food for anaerobic bacteria, which releases gas and liquid components. The gas is dispersed through the plumbing system vents in the house, or tank and drainfield vents. Solids do accumulate in the septic tank. The tank must be serviced (pumped out) every 1 to 3 years or whenever the solid component of the tank exceeds 1/3 of the tank’s volume to reduce the chance of solid material flowing into the drainfield.

Grease and other floating solids are prevented from flowing out of the tank by a baffle, filter or “T” located on the inside of the tank at the outlet end. Another baffle is placed on the inlet side of the septic tank. This forces the incoming waste down into the tank, which prevents short-circuiting across the top. These baffles can deteriorate over time and must be checked at each tank servicing. There are tank baffle filters (known as the Zable filter) available that can prevent the smallest suspended particles in wastewater from getting into the drainfield, which may cause premature drainfield clogging. These filters must be maintained ever 6 months or once a year.

Where there is known to be excessive amounts of grease in the waste, typical with restaurant waste, a minimum 2 septic tank design is use with the 1st tank deemed the “grease trap”.

Pressure Distribution
Gravity Flow

The drainfield is the final and most important step of the effluent treatment and disposal. The size, elevation, location and shape of the drainfield is all relative to the expected usage.

The drainfield sizing is determined by the flow from the house (number of bedrooms) and the type of soil. Usually the more previous the soil the smaller the drainfield, however, a certified soil tester makes this determination based on the many physical features within the soil such as texture, structure, consistence and layering of the soil. The elevation and location of the drainfield is determined by the type of soil at various depths and/or the elevation of the seasonal water table, saturation zones within the soil, or bedrock.

A drainfield design using trenches are narrow beds has been shown to improve aeration in the underlying soil thereby enhancing treatment of the effluent and drainfield longevity. When there are several trenches or beds, a distribution box may be incorporated to promote equal distribution of effluent.

Pressure Distribution

These systems require a pump to force the effluent into the entire piping network and out holes that have been drilled in a small diameter pipe. This force is a precise calibration based on the pump flow, head pressure, lift elevation, distance and perforation diameter and number. When a pressure distribution drainfield is far enough downslide from the septic tank, a tank with a siphon may be used to force the effluent through the system instead of a pump. A siphon must be checked periodically to ensure that it is properly discharging effluent in doses rather than “trickling” effluent into the drainfield.

Gravity Flow

This non-pressurized distribution consists of interconnected 4inch diameter piped having numerous holes larger than ½ inch on each side. Non-pressurized drainfields work on the principle of “progressive ponding”. That is all of the effluent trickles into the drainfield gravel through only a few holes and eventually overloads the soil below at the point. Then the effluent spreads out from that point to the surrounding soil until, over time, the entire drainfield is ponded. This ponded condition is due to the accumulation of biomass and slimes as a clogging layer at the gravel-soil interface produced by anaerobic bacteria, which thrive under, saturated conditions.

As a clogging layer thickens more effluent ponds above it since more volume is required to force through this layer. In the end the effluent level with the drainfield rises onto the ground surface or backs up into the house depending upon which is lower in elevation. If there is a pump tank the pump may be running constantly if the drainfield will not accept liquid. A critical time for this first occurrence is in the spring once the frost has melted and snowmelt increases the moisture content within the soil. A homeowner should contact a septic tank pumper immediately to prevent further discharge and proceed with a replacement drainfield.

There are 6 different ways, reasons, and things that would shorten the life of a drainfield:

  1. Overloading. If the drainfield is undersized for the current usage, early ponding or saturation will occur. A leaking plumbing fixture may add hundreds of gallons of water per day to the drainfield. An undersized septic tank will not adequately allow for sufficient holding time to settle out the solids and grease, which can then flow into the drainfield and cause clogging. Doing all the clothes washing on one day may overload a septic system. This is referred to as surge loading when one day a high usage of water occurs verses lower use the rest of the week. Septic systems should be sized for the anticipated surge load.

  2. Grease. In the septic tank the type of bacteria that lives, eats and multiplies does not thrive in solidified grease. Animal fats solidify at room temperature. You have seen this inside a pan left on the stove after frying bacon or hamburgers. As soon as the fat remaining in the pan cools, it becomes a gray, solid mass.

    This same thing happens when the leftover fat is poured down the sink drain or into the garbage disposal. It begins to congeal in the sewer line to the septic tank or form a solid mass inside the tank. Eventually, the sewer line becomes constricted or completely closed up. The septic tank will have accumulated a large mass of solid fat, which cannot be broken down by bacterial action. Most people assume that the “pipes are clogged”. Then they dup the commercially prepared crystal powder or liquid drain “openers” down the drain.

    These strong chemicals can kill off the septic tank bacteria reducing the effective breakdown of solids within the tank. Grease should be treated as garbage and kept out of the septic tanks whenever possible.

  3. Sanitary Napkins, Condoms, Cotton Swabs, Dental Floss, Tampons, Hand Wipes, Infant Wipes, Disposable Diapers and Cigarette Filters. These products are made of cellulose, plastic or other non-biodegradable components. They may plug the sewer lines, baffles and drainfield perforations or lodge in the pump. Pressure distribution networks, having narrow pipes and small diameter holes, are especially sensitive.

  4. Antibiotics, Other Medicines, Disinfectants, Painting Products, Gasoline, Oil, Degreasers and Pesticides. When disposed of through the septic system these chemicals may kill septic tank bacteria. This can result in a severe decline in decomposition of the septic tank solids. It can take several weeks for the bacteria in the septic tank to reestablish. This can increase the solids buildup in the tank and carry over into the drainfield. Volatile compounds, such as petroleum products, and accumulate in the soil and may enter into the groundwater.

  5. Clear Water Discharges. Building foundation drains as well as humidifier and water softener discharges are considered clear water, which may be disposed into the ground separate from the septic system. Discharge from the softener during the recharge cycle is a salt brine, which in excessive amounts could have an adverse effect on septic tank bacteria.

  6. Surface Drainage. After the installation of septic system, the finished grade of the ground surface will be slightly mounded to direct away any surface flow of water. This is done to prevent rainwater from competing with effluent at the infiltrative surface within the drainfield.

    Over time this mounded area may settle and actually sink below the natural grade of the surrounding landscape. This could result in surface water from rain or snowmelt entering the drainfield area or seeping into the septic or pump tanks. The result is the same as overloading of a septic system and should be corrected immediately, roof downspouts, driveway runoff and road ditches should be directed away from the septic system.

    Your septic system can do its job economically and safely. Most communities have installation contractors who can inspect your system periodically to insure its longevity.

WARNING! Never enter the septic tank. The Septic tank produces gases, which can kill a person in a matter of minutes. Never go into a septic tank to retrieve someone. Call for emergency services and put a fan at the top of the tank to blow in fresh air.

Frequently Asked Questions

How often should I have my septic tank pumped?

That depends on 3 major factors:

  1. Capacity of the tank
  2. Volume of wastewater (related to size of household)
  3. Amount of solids in wastewater (e.g. garbage disposal produce more solids)

The following table lists estimated pumping frequency according to septic tank capacity and household size. The frequencies were calculated to provide a minimum of 24 hours of wastewater retention assuming 50 percent digestion of the retained solids.

Tank Size Household Size 

Years Between Pumping

Years Between Pumping layout

**Note if you live in Dane county Wisconsin the County does require that you have the system either pumped or inspected every 3 years. If your sludge level in the bottom of the tank is 2/3rds the capacity of the tank it is a mandatory pumping.

What are the warning signs of a failing septic system?

These signs may be indicators that the drainfield is failing:

  1. Any plumbing backups
  2. Grass in the yard growing faster and greener in the area of the drainfield or tank(s).
  3. Soft or mushy ground in the area of the drainfield.
  4. Constant sewage odors
  5. Sluggish toilet flushing.
  6. Septic pump runs constantly
  7. Solids accumulating in the drainfield vent or observation tubes.

Can garbage disposals be used with septic systems?

Yes, but try to avoid allowing grease or slowly biodegradable products such as course fruit and vegetable peelings and bones to get into the disposal.

What can I plant over my drainfield?

Grass is the ideal cover for drainfields. Grasses can be ornamental, moved in the traditional lawn, or in an unmoved meadow. Or you can try groundcovers and ferns. The key to planting over the drainfield is to select shallow rooted, low-maintenance, low-water-use plants. For those whose tank-covers are buried, keep in mind that the plantings over the tank - from inlet to outlet - will have to be removed every 3 years for inspection and pumping.

How close can trees and shrubs be to the drainfield?

Trees or large shrubs should be kept at least 30 feet away from your drainfield. If you do plan to plant trees near a drainfield, consult an expert to discuss your ideas and needs. Trees and shrubs generally have extensive root systems that seek out and grow into wet areas, such as drainfields.

Plants you can grow on standard drainfields: deep shade (receives no direct sun)

  • Carpet Bugle (ajuga reptans): an aggressive groundcover with blue flowers in the spring
  • Japanese Spurge (pachysandra terminalis): an aggressive evergreen groundcover; once established, it forms a thick cover, minimizing weeds
  • Periwinkle (vinca minor): an evergreen groundcover with periwinkle blue flowers in the spring. Moderately drought tolerant in shady areas.
  • Sword Fern (polystichum munitum): a native evergreen fern that in a shady location is very tolerant of our dry summer months, easy to grow.
  • Irish Moss (sigina): not a true moss, but a good look - alike and much easier to grow. Does best when mixed with ferns and other plants.

Note: do not mix carpet dugle, Japanese spurge and periwinkle - select one.

Partial sun and shade (received about four hours of afternoon sun)

  • Blue Star Creeper: an attractive, fast - growing groundcover with tiny blue flowers.
  • Vaccinium “Well’s Delight” (vaccinium grass folium): shiny, dark evergreen leaves with dainty pinkish flowers, a good, three inch tall groundcover for partial sun.
  • Creeping Rubus (Rubus pendulous): this is a species of ornamental bramble, but its leaves and small flowers are much more decorative than its thorny cousins. The rooting caret of stems can easily grow four feet a year.

Sun (received full sun all day or about eight hours)

  • Kinikinnick (arctostaphylos uva-ursi): a native evergreen groundcover known for its drought tolerance once established. Requires well - drained soil; not tolerant of wet areas.
  • Blue -silver fescue (festuca cinema): an ornamental grass with blue - sliver blades. A short, clumping grass requiring well - drained soil, not drought tolerant
  • Blue oat grass (helictotrichom sempervirens): an ornamental grass with stiff evergreen blue blades. Requires well- drained soil.
  • Fountain grass (pennisetum alopercuroides): an attractive fountain grass with arching stems bearing soft, bottlebrush clusters of fuzzy flowers. Grows to about 1 ½ to 2 feet and is tolerant of moist soils, unlike some other ornamental grasses.

What type of plants can I plant near a mound?

For a mound system the best plants would be wildflowers and or grasses. Here is a list of plants in each of these two categories.


  • Prairie onion (Allium stellatum)
  • Pussytoes (Antennarie naglecta)
  • Butterfly weed (Asclepias tuberose)
  • Heath aster (aster ericodes)
  • Bigleaf aster (aster macrophyllus)
  • Pennsylvania sedge (carexpensylvanica)
  • Prairie clover (dalea spp.)
  • Pale purple coneflower (Echinacea angustifolia)
  • Rattlesnake master (eryngium yuccifolium)
  • Wild geranium (geranium maculatum)
  • Prairie smoke (geum triflorum)
  • Oxeye (helianthus helianthoides)
  • Rough blazing star (liatris aspera)
  • Wild bergamot (monarda fistulosa)
  • Penstemon (penstemon spp.)
  • Pasqueflower (pulsatilla patens)
  • Violets (viola spp.)


  • Sideoats grama (bouteloua curtipendula)
  • Blue grama (bouteloua gracilis)
  • Little bluestem (schizachyrium scoparioum)
  • Prairie dropseed (spurious heterolepis)
  • June grass (koeleria macrantha)

These plants are propagated by seed or plants. A combination of both will make a faster cover. Use a mulch of clean straw or a cover crop of annual ryegrass or oats to prevent erosion while the plants become established.

What if liquid is observed in the drainfield vent or observation tubes?

Liquid observed in the drainfield usually indicates that the soil absorption capability of the drainfield is reduced and ponding in progressing. Many systems begin ponding within the first 6 years. The ponded state of a drainfield is usually a slowly developing condition. The estimated life of today’s drainfields under normal usage is 15 to 25 years. If there is sludge in a vent pipe or observation tube this is an indication of a serious condition.

Which laundry detergents are the best for a septic system?

Laundry detergents contain emulsifier - some brands more than others. An emulsifier suspends fats, grease and oils in water for a time - usually the time it takes to pass out of the septic tanks. These components may congeal in the sewer lines and drainfield. It’s always best to not overuse any detergent. Avoid detergents containing phosphates to protect the groundwater. It is always best to also use liquid detergents.

What can I do to prolong the life of my drainfield?

There are several things you can do:

  1. Install water - saving devices and be on-guard for leaky fixtures
  2. Have the tank(s) pumped and inspected regularly
  3. Keep surface water away from the septic system area including the septic and pump tanks.
  4. Keep driveways, parked vehicles and buildings off the drainfield area. Soil compaction can cause premature failure by restricting the infiltrative and evaporative capability of the soil
  5. Install a second septic tank to further reduce solids from entering the drainfield
  6. The use of pretreatment alternatives such as aeration tanks have been shown to improve effluent quality and moderate or reduce ponding.
  7. Understand what can and cannot be put into the septic tank. 
  8. Use 1 ply toilet paper. It is better to use more of that then it is to use less to the plush stuff. Never use paper that has lotions or perfumes as these do not break down in the septic tanks
  9. You can use bleach just not a lot, this will kill the bacteria
  10. Use liquid laundry soap. Watch the use of anti-bacterial hand soaps
  11. Never put grease down your sink. The only grease should be what would come off the dishes that are washed in the sink.
  12. Do not flush sanitary products or condom down the toilet.

What is a Mound System?

A Mound System incorporates an above grade drainfield containing a pressurized distribution of effluent. The drainfield is elevated to maintain a proper separation between the effluent discharge and some limitation (such as bedrock) below it. The original topsoil is plowed and covered with a required amount of approved medium to course sized sand. Within this sand mound a gravel bed is placed containing the distribution piping.

What is the Wisconsin Fund?

The Wisconsin Fund Grant Program provides financial aid incentives to protect and improve water quality in the Sate of Wisconsin. The fun provides grants to assist homeowners and small businesses in the rehabilitation or replacement of their failing sewage systems.

Certain criteria must be met as to ownership, income levels and degree of failure. Contact your county health or zoning department as to current requirements as these change yearly. Generally this grant must be applied for previous to installation or repair of a septic system.

We hope this information will help you and your family in the care of your septic system. This system needs care and maintenance much like any other component of your home. Installing a new septic system or replacing a drainfield can be expensive, but remember that you now have a modern, economical sanitary wastewater recycling system, and there is not sewer tax to pay!