​Septic systems come in different shapes and sizes depending on their age and design. All liquid from your home, including the laundry, bathroom, and kitchen should drain into the septic system.

Below are 3-D septic models (Thank you to Tacoma Pierce County Public Health and Sketchfab.com). They are great illustrations of the different types of systems, their parts, and how they work. Go to Wastewater Forms and Publications for more information from Washington Department of Health.

Models Provided by Sketchfab via Tacoma Pierce County Health Department www.sketchfab.com/tpchd.

How It Works

The drainfield is a network of perforated pipes (or "laterals") laid in gravel-filled trenches or beds. After solids settle in the septic tank, the liquid wastewater (or effluent - the liquid discharged from a septic tank or other on-site sewage system component) is discharged, either by gravity or pressure, to an absorption field, also known as a drainfield or leach field. NOTE: In most gravity systems the wastewater first flows into a distribution box (d-box) or tee, which then disburses the effluent equally among the trenches in the drainfield, which is where the final treatment takes place.

• Landscape Your Drainfield — Planting tips and other landscaping information.
• Landscape Your Drainfield (Spanish)
• Landscape Your Drainfield (Vietnamese)
• Landscape Your Drainfield (Korean)
• Request for Record Drawing

Effluent trickles out of the pipes, through the gravel layer, and into the soil where further treatment occurs. The soil filters the wastewater as it passes (or "percolates) through the pore spaces and the soil microbes treat it before it eventually enters the groundwater. These processes work best where the soil is somewhat dry, permeable, and contains plenty of oxygen for several feet below the drainfield.

The drainfield is generally located in a stretch of lawn in the back or side yard of a property. The size and type of drainfield depends on the estimated daily wastewater flow and local soil conditions.

The Soil

The soil below the drainfield provides the final treatment and disposal of the septic tank effluent. After the wastewater has passed into the soil, organisms in the soil treat the effluent before it percolates downward and outward, eventually entering ground or surface water. The type of soil also impacts the effectiveness of the drainfield; for instance, clay soils may be too tight to allow much wastewater to pass through and gravelly soil may be too coarse to provide much treatment.

Replacement (Reserve) Area

Every new home or building served by a septic system is required to have a designated replacement or reserve area. This is a designated area suitable for a new drainfield and must be treated in the same manner as your existing drainfield. (A reserve area should have been designated as part of the permit process for any sewage system installed since 1980.)

Once a septic system has failed, it is too late to solve the problem by pumping your tank. A new drainfield will have to be installed at a different location. This is why it is important to know where the replacement area is located and how to protect it (see "Drainfield Do's and Don'ts" for replacement area care). 

Drainfield Do's and Don'ts

Do These Things

• Know where your drainfield and replacement area are located. When you know where it is located, it is easier to protect. 
• Keep heavy equipment off your drainfield. Cars and heavy equipment should not park or drive over the drainfield; doing so can crack pipes. Create a barrier if accessible to cars, livestock, or heavy equipment.
• Keep water usage to a minimum. Drainfields do not have an unlimited capacity. When there is more water than it can absorb, the system is unable to drain and filter effluent before it reaches groundwater.
• Divert water away from the drainfield. Water runoff from roofs and drainage ditches can saturate the soil. Drainfields are most efficient when the soil beneath the drainfield is not saturated.
• Keep trees and shrubs at least 30 feet away from the drainfield. (NOTE: Some soil conditions may require that plantings be kept an even greater distance from the drainfield.) Trees and shrubs generally have extensive root systems that seek out and grow into wet areas, such as drainfields. This can lead to clogged and damaged drain lines. For more information, see Landscape Your Drainfield.
• Plant only grass or shallow-rooted plants over the drainfield. This will prevent soil erosion.
• Protect your replacement area. It may be the only area with acceptable soil conditions in case you need to replace, repair, or add on to the drainfield. All of the above suggestions apply to the replacement area as well.

Don't Do These Things

• Don't build over your drainfield. This includes patios, carports, and other structures. You may damage the drainfield.
• Don't pave over the drainfield. Drainfields need air to function properly. Oxygen is needed by bacteria to break down and treat sewage.
• Don't dig in your drainfield. Damage to the pipes can occur.
• Keep large animals and livestock off the drainfield. Soil compaction prevents oxygen from getting into the soil and prevents water from flowing away from the drainfield.
• Don't use landscaping plastic over the drainfield. Air is necessary for the drainfield to function efficiently.
• Don't plant a vegetable garden over a drainfield. You risk the possibility of food contamination.
• Don't install an irrigation system in the drainfield. Neither should the irrigation system drain toward the drainfield.

You know your septic system drainfield is out there… but just where is it? It is important to locate it so you can avoid damaging it by:

• Paving over the drainfield
• Parking or driving heavy equipment over the drainfield
• Planting trees or shrubs too close to the drainfield
• Disturbing the soils with a landscaping project or livestock

It is also important to know where your drainfield is located, so you can check the drainfield for problem signs, such as soggy soil and odors.

Record Drawing

Get a copy of the record drawing for your system. The septic system "record drawing" (previously referred to as an "as-built") is a diagram showing where your septic system components are located.

You can download the Request for Record Drawing/Permit Information or contact the Thurston County Building Development Center (BDC), 360-786-5490. The BDC is located at 3000 Pacific Ave SE, Olympia, on the first floor (BDC Hours of Operation). When you call or visit, please have your eleven-digit tax parcel number ready. This is the number that appears on your county tax statements. (If you do not have your tax parcel number, contact the County Assessor's office.)

The quality and detail of record drawings vary greatly. An older diagram (prior to 1980) may be a very rough, simple sketch showing the layout of your system. A newer diagram will show the tank, drainfield, replacement area (for future use if a replacement field is needed), and any other components of your system, such as a pump chamber or mound. The size of the tank and length of the drainfield lines may also be noted.

Tips to Locate Your Drainfield

If a copy of your record drawing is not available, try the following tips to locate the drainfield.

• In late summer, if you stop watering your lawn you may see green stripes in your yard. These are the damp areas along the drainfield pipes. In the winter, the areas above the pipes may be the first place frost melts in your yard.
• Do you have monitoring ports or clean-outs? These are white-capped tubes or pipes, cut off at or near the ground surface. They allow you to check the liquid level in the drainfield pipes and are located at the ends of the pipes.
• Carefully probe the areas leading away from the septic tank. Avoid using heavy steel wrecking bars or similar probing tools that can damage the septic tank top or other components.
• Look for clues such as shallow, parallel depressions, which may mark the drainfield trenches. It is unlikely that a drainfield could have been installed among large trees or in very rocky areas.
• Go under the house and look where the sewer pipe exits the foundation. The septic tank is usually within 10 feet of the foundation.
• Hire a professional company to send echo-locators down.

For more information on troubleshooting problems,
contact the Septic Help Line at 360-867-2669.

​The most important step to maintaining your septic tank is to remove sludge and scum build-up before it washes into the drainfield. How often your tank needs pumping depends on the size of the tank, the number of people in your household, the volume of water used, and amount of solids (from humans, garbage disposals, and any other wastes) entering the system. Generally, tanks should be pumped every 3 to 5 years. See Septic Inspection and Pumping Guide.

PLEASE NOTE

Thurston County does not regulate the business practices of certified contractors.

Get several estimates, check references, and be clear what services are being requested before hiring a contractor.

Pumping and Inspection Guide

It is best for your system to use less water. The more wastewater you put down the drain, the more liquid the system must treat and dispose of.

To reduce your water use:

• Use water saving devices on your showerheads, toilets, and faucets.
• Repair leaking faucets and plumbing features. A leaking faucet can be slow or hard to see but can add up to hundreds of gallons of extra water for your system.
• Don't leave the water running when brushing your teeth or washing your hands.
• Take shorter showers.
• Only run the laundry machine or dishwasher when it is full. If your laundry machine has load size settings, use the correct load size for laundry you add.
   
  • Water Savings Tips from Thurston PUD
  • Every gallon of water you save, saves you money

Other conditions that put added stress on the system include the arrival of an infant or extended holiday visits from relatives or friends. Consider having the system inspected more often during times of high use and pump as often as needed.

What goes down the drain can have a major impact on your septic system. Many items don't break down and will fill up your septic tank. Most items can go in the garbage or compost instead of into your system.

Do not put extra waste down the toilet.  It is not a trashcan. Only human poop, pee, toilet paper, and soaps for washing should go down the drain. Anything you flush down today will have to be pumped out later!

Never flush:

​Septic systems rely on a healthy population of bacteria. Adding chemicals to the system can hurt the bacteria that make a septic system work properly. Septic systems do not remove the chemicals you flush. Chemicals pass through the system and can be harmful to the environment.

Additives do not reduce the need for regular maintenance and often claim to reduce the scum and sludge in your tank which will limit pumping costs. Additives have not been tested to determine if they work. Additives are expensive and may cost more than the routine pumping your system will require.
 

Washington State Department of Health (WA DOH) maintains a list of Approved On-site Sewage System Additives. The list is designed to ensure all additive chemicals are safe to use, WA DOH does not test if the additive works. 

​Septic tanks are mainly settling chambers. They allow time for solids and scum to separate out from wastewater, so clear liquid can safely go to the drainfield or pump tank. Over time, the scum and sludge layers get thicker, leaving less space and time for the wastewater to settle before passing to the drainfield.

For every gallon entering the tank, one gallon is pushed out into the drainfield. So it is important to keep the level of scum and sludge from building up and nearing the inlet or outlet baffles, where the scum or sludge could plug them up or be carried out to the drainfield or pump tank.

Septic tanks should be checked for buildup every 1 to 3 years until you can get on a predictable pumping schedule. Most septic tanks need pumping every 3 to 5 years. How often depends on the size of the tank, the number of people in the household, and the amount and type of solids entering the tank.

You can hire a professional or inspect your septic tank yourself. The "stick test" procedure will guide you through the steps of measuring the amount of scum and sludge in the tank, discovering the working capacity of the tank, and determining whether the tank needs pumping. A more complete inspection includes inspecting the condition of the baffles and the pipe seals into and out of the tank.

     Stick Test and Baffle Inspection Video Instructions  (WADOH)

The "stick test" is a simple way of measuring the amount of scum and sludge in the tank for when pumping is needed. While measuring the scum and sludge we recommend you also inspect the baffles. Below are instructions on how to make the sticks and perform the stick test:

Items needed to make the scum and sludge measuring sticks.     

Make two inspection sticks. One stick to measure scum and one stick to measure sludge.

Step by Step Instructions

Step 1: Remove the Tank Lid

Remove the septic tanks first compartment lid, it will be about 2ft in diameter.

Use your record drawing to help find where your septic tank is located.

Some systems have "risers" that bring the tank lid up to the surface of the ground so digging is not needed. If your tank does not have risers, you must dig up the septic tank lids or hire someone to dig up the lids before inspection. Digging up the lids can be expensive and deep tanks without risers can be more difficult and dangerous to inspect yourself.

Step 2: Measure the Scum Level

Measure the thickness of the scum level, the floating layer on top of the liquid in the tank.

1. Lay a board across the top of the hole, manhole, or riser.
2. Place the scum stick down the manhole of the first compartment of the tank until it rests on top of the scum layer.
3. Use the pen or sharpie to mark the scum stick where it crosses the board.
4. Push the elbow end of the stick straight through the scum layer, turn the stick 90°, pull slowly up on the stick until you feel resistance from the bottom of the scum layer. Stop.
5. Use the pen or sharpie to mark the scum stick where it crosses the board.
6. Remove the scum stick and measure the distance between the two marks. This is the thickness of the scum layer.

Step 3: Measure the Sludge Level and Working Depth

This procedure determines the thickness of the sludge level.

1. Lay a board across the top of the hole, manhole, or riser.
2. Lower the sludge stick into the first compartment of the tank until it rests on top of the liquid layer.
3. Mark the stick where it crosses the board.
4. Make a hole in scum to put the sludge stick through.
5. Lower the stick to the bottom of the tank.
6. Mark the sludge stick where it crosses the board.
7. Hold the stick in the tank for at least five minutes to allow sludge particles to adhere to the Velcro.
8. Carefully remove the stick.
9.  Measure the distance between the two marks. This is the working depth of the tank.
10. Measure the length of the dark staining on the velcro, this is the depth of the sludge layer. 

Disinfect your Scum and Sludge Sticks

• Wear rubber gloves.
• Rinse sticks with a solution of 1:10 bleach and air dry.
• Put soiled gloves and used towels in a plastic bag and discard in the trashcan.
• Wash your hands

Step 4 — Inspecting the Baffles (optional)

Remove the lids over the baffles: inlet, outlet, and the crossover baffle which is only found in two or three compartment tanks.

Look at the baffles to check:

1. They are present.
2. They are in good condition and not cracked, chipped, or severely corroded.
3. PVC inlet and outlet baffle are sealed to the tank.
4. Concrete baffles should have venting holes.
5. The crossover baffle should be free of obstruction.

Step 5 — Determine if Pumping is Needed

After you measure the scum, sludge, and working depth, determine if pumping is needed. Pumping is needed if you add the scum and sludge together and they are bigger than one-third (33%) the working depth.

Below is a formula to help you determine if you need to pump. Put the inches of your scum, sludge, and working depth into the boxes below and click submit.

Pumping Needed

The results show your tank is XX% full of scum and sludge and pumping is needed. Contact a septic company to have them pump your septic tank. If you have more than one compartment in your tank, all compartments must be pumped. 

Routine checking of the scum and sludge levels will help you determine how quickly the levels are growing in your system and when pumping may be needed next. If the scum and sludge are building up quickly in the tank, we recommend looking at your activities inside the home.

Pumping Not Yet Needed

The results show your tank is XX% full of scum and sludge and pumping is not yet needed. Check your levels again in 6-months to one year to see if pumping is needed. Routine checking of the scum and sludge levels will help you determine how quickly the levels are growing in your system and when pumping is needed next. 

​Like an automobile, your septic system also requires maintenance to function properly. Most systems that fail prematurely are due to improper maintenance.

If you notice any of the following signs or if you suspect your septic system may be having problems, contact a qualified septic professional. Should your septic system fail, contact Thurston County Environmental Health at 360-867-2673.

 

 

• Odors, surfacing sewage, wet spots, or lush vegetation growth in the drainfield area
• Plumbing or septic tank backups (often a black liquid with a disagreeable odor)
• Slow draining sinks and tubs
• Gurgling sounds in the plumbing system
• If you have a well and tests show the presence of coliform bacteria or nitrates, your drainfield may be failing
• Lush green grass over the drainfield, even during dry weather

Excessive water in the drainfield causes the septic system to overload, slowing down or stopping the treatment of wastewater. When this occurs, you run the risk of your septic waste backing up into your home, particularly if your drainfield is partially clogged. Although it may work well during dry weather, in wet weather, a rain-soaked drainfield may be too saturated for the effluent to percolate down through the soil.

During flooding or heavy rains, it is prudent to reduce, and in some cases, stop using your septic system. If you are affected by the threat of flooding, there are certain things you can do during a major rain or flood:

• Conserve water usage and reduce toilet flushing until the system is restored to working order.
• If your drainfield is covered with water, do not use the system until the water has receded.
• If you have a pump, turn off the electricity.
• Make sure there is no damage to electrical connections before turning the system back on.
  NOTE: Be sure to turn the pump on before using the system.
• If silt and debris have gotten into your septic tank, have the system pumped as soon as possible. NOTE: Wait until the water has receded and the area is no longer saturated before opening the tank.
• If any sewage has backed up into the house, avoid contact with it. Disinfect thoroughly to prevent serious illness from the disease-causing organisms in the wastewater.
• Check for blockages. It is possible the outlet tee (or baffle) may be partially plugged due to floating scum that floated up during the flooding.
• If you use a well for drinking water and flooding came up to the well casing, do not drink the water. If the water is murky, have it tested before drinking.

Contact a septic system professional, if any of the following problems are present:

• Water over the drainfield that does not recede after the rain stops.
• You smell a sewage odor.
• Wastewater or sewage backs up into the house.
• Slow running drains, especially after doing laundry or taking a shower.
• You notice soggy areas with surfacing sewage in your yard.

Direct water from downspouts and roofs away from the drainfield. Additional water from these sources may prevent your drainfield from working properly.

Keep cars and trucks off the septic tank and drainfield areas. This prevents pipes from breaking and soil from becoming compacted. Compacted soils can't absorb water from the drainfield.

Don't construct patios, carports or use landscaping plastic over the drainfield. Grass is the best cover for your septic tank and drainfield. Soil compaction and paving prevents oxygen from getting into the soil. This oxygen is needed by bacteria to break down and treat sewage.

Protect your drainfield from intrusive shrub and tree roots. Only allow plants with shallow roots to grow over and near the drainfield. Choose plants that are low-maintenance and low-water using. See Landscaping Your Drainfield.

Unless you have a gravity septic system (which does not require electricity and continues to operate efficiently even when the power is off), most other systems are dependent upon electricity to run the pump or other electrical components.

• Keep water use to a minimum, especially if the system has a pump. The septic tank can hold about one-day's supply of waste. Once the tank is filled, additional waste can back up into your home.
• Turn off the pump at the control panel. Effluent will continue to build up in the pump chamber until it resumes operation.
• After power is restored, switch the pump on and let it run for 5 minutes maximum; turn it off again.
• Repeat this manual switching every 6 hours until the effluent drops to the "OFF" float level and the pump turns off automatically. If there is little water use during the outage or pump service, the pump may automatically turn off during the first manual switching.

CAUTION: Do not enter the pump chamber. Gases inside pump chambers are poisonous and the lack of oxygen can be fatal. Always turn off the power supply at the circuit breaker, and unplug all power cords before handling the pump or floats. The service or repair of pumps and other electrical equipment must be done by an experienced person.

Conventional Systems

• Gravity System 
• Pressure Distribution System 

Alternative Systems

• Aerobic Treatment Unit (ATU) 
• Mound System 
• Sand Filter System 

Other Systems (Proprietary)
For the most up-to-date information on proprietary sewage products approved by Washington State, see the Washington State Department of Health document titled "List of Registered On-Site Treatment and Distribution Products"

• ​Gravity
  • Gravity (Spanish)
  • Gravity (Vietnamese)
  • Gravity (Korean)
• Pressure Distribution
  • Pressure Distribution (Spanish)
  • Pressure Distribution (Vietnamese)
  • Pressure Distribution (Korean)
• Aerobic Treatment Unit (ATU)
• Mound System
• Sand Filter System
• Other Proprietary Devices - for the most up-to-date information on proprietary sewage products approved by Washington State.
• Septic System Tips
  • Septic System Tips (Spanish)
  • Septic System Tips (Vietnamese)
  • Septic System Tips (Korean)

DIY Septic System Inspection Video (WA DOH)