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COLORADO ONLY - plastic triple-wall Infiltrator brand heavy-duty septic tank kits.
Click here for main septic chapter with other system parts and pricing.

"Are we allowed to install this septic system on our property" is not a question we can answer for you. We have been providing much the same passive (non electric) septic system parts for over twenty years now, but we do not follow constantly changing city, county, and state building regulations. Unfortunately, with 63 counties in Colorado, regulations changing from year-to-year, and interpretations of those rules varying from one inspector to another, it's never possible to say for certain 'what is allowed' locally. The county building department is your primary source of information on what is possible to install according to local 'code'. Rather than telephone them with questions, you should drive over in person and get a copy of their local Individual Sewage Disposal System ISDS Regs and also get a list of locally licensed soil engineers. The building department will confirm or revise your site plans once submitted for approval. Often the county inspector will assist you with site plans and design as a service provided for their permit filing fee. If not, they will refer you to a local engineering firm that can visit the property in person and design the system. We provide free consultation after the sale on installation procedures, system design improvements, and operational issues, but we do not provide any soil testing, on-site services, 'stamped' engineered plans, or 'advanced treatment' systems.

Conventional septic tank with leach field guidelines along with some tips and tricks...

Septic tank specifications, installation details, tips and tricks

Georgia Co-Operative Extension Service's septic system manual serves as a good outline for any conventional septic tank system

Septic tank sizing is best determined by usage and how long effluent stays in the tank before it goes out to the leach field. Consider a thirty hour sewage treatment retention time to be the minimum, with larger tanks allowing more time for solids to settle on the bottom and grease to float to the top. Less daily flow means more clarified liquid receiving treatment prior to disposal in the leach field. Best practice is to install at least a 1250 net gallon two-compartment tank. In the long run, you save money by having the septic tank pumped less often and the leach field is less subject to bio-mat formation due to untreated, less-clarified effluent.

Slower percolation rates due to poorly draining soil with clay, bedrock, high ground water, proximity to a creek, or other complications require larger leach fields. There are two methods of calculating the minimum absorption area for a leach field. Traditionally, you dig an eight foot deep test inspection hole in the area of the intended leach field to allow building inspector, or your local engineer, to physically examine the soil and determine its Long Term Acceptance Rate. Or you can have a local soil testing firm perform a percolation test to clock the speed of your soil's capacity to absorb liquids. Local building code dictates the equation used to calculate how many square feet of leach field is required based upon the speed of percolation, composition of the soil, and LTAR. A general rule-of-thumb to use when estimating is one square foot of leach field, per gallon of effluent, per day, in normal soils that percolate relatively well.

conventional septic system manual
courtesy of Georgia Co-Op Extension Service 540kb .pdf

Please note that we are not Infiltrator®, the manufacturer, and we do not ship Infiltrator plastic septic tanks or Infiltrator chamber leach field systems outside the state of Colorado. Infiltrator chambers and plastic triple wall septic tanks are only delivered within about 50 mile radius of Denver (North to Loveland, South to Castle Rock, up to Georgetown, and out East to Byers) or provided will call, pickup in person at the Commerce City warehouse. Motor freight for such large items has become so expensive we no longer quote out-of-state shipments of septic tanks and chamber systems, but any local distributor of plastic storage tanks and PVC pipe is capable of sourcing septic tanks and chamber systems for your project. For local referral, please contact the manufacturer direct at: e-mail: or phone: 800-221-4436.

Save money by renting a backhoe and installing your own plastic septic tank for your home sewage system. Should local code dictate installing a concrete septic tank, have it seal-coated well and try to avoid rectangular vaults, as the rounded end, hockey rink shape, is much stronger. Unlike concrete, plastic tanks are not affected by high ground water and saturated soils which will eventually erode concrete, forcing replacement. Plastic has many advantages over concrete in addition to durability in wet locations: consistent quality, portability without a crane truck, and three-way inlet and outlet ports. Polyethylene tanks will never crack (and leak) and they are easily moved around by two people, saving money on heavy equipment and making difficult locations easier to build.

Septic tank size depends entirely upon local building code requirement, which is spelled out in the Individual Sewage Disposal System ISDS regulations for your area (local building code). Every county has its own unique regulations with equations and definitions that can change yearly and always are open for interpretation. In practice, a 1250 gallon, two compartment, septic tank is considered the minimum size requirement for an up to three bedroom home, with at least 1500 gallon recommended at four bedroom. While 1000 gallon tanks are available, any cost savings is quickly lost from increased pumping frequency and greater chance of leach field contamination from undigested solids. The larger the septic tank, the slower and more thoroughly it processes the solid waste.

The wastewater your home produces is referred to as effluent and consists of blackwater (toilet waste) and greywater (kitchen, shower, sink, and laundry waste). Effluent flows directly from your house into a watertight, underground, two compartment septic tank where solid waste settles into a sludge layer on the bottom and fats float to the top. Between these two scum layers is a zone of clarified liquid effluent that is internally piped to the second compartment of the septic tank for additional settling. As effluent fills the first compartment, clarified liquids are forced to leave the second compartment of the sewage tank and flow out to the leach field. Without this two compartment design, with divider/partition/baffle, solids might be able to leave the tank and enter your leach field, eventually clogging the soil pores and resulting in leach field failure someday.

$2325* delivered price - Infiltrator TW1250 1250 gallon, triple wall, two compartment septic tank kits
$2580* delivered price - Infiltrator TW1500 1500 gallon, triple wall, two compartment septic tank kits
$250 less for just the septic tank by itself (no manway risers or installation kit with fittings and filter)
* 3% discount when paid with cashier's check or postal money order ... free delivery within about 50 miles of Denver or pickup at warehouse

Please note these prices are for the full kit, which traditionally includes tank, two 12 inch tall manway risers, inlet and outlet gaskets, 5 inch hole saw kit, threaded cleanout for pipe from house, tank inlet fittings, and septic outlet filter with housing and handle. Price also includes delivery within up to about 50 mile radius of Denver or will-call, pickup in person, at our Commerce City warehouse. Plus, we're here to help every step of the way, doing our best to ensure you don't make that one critical mistake, like not using risers or not venting your leach field properly. We encourage clients to mail copies of their septic system permit plans for our review after purchasing a system, as there are always details that could use improvement with any plan. Infiltrator tanks are UPC listed for permit approval ease, come with a fifty year warranty, and are triple wall with deeply ribbed sides for the extra support needed to be buried up to four feet underground.

click here for Infiltrator® Systems TW series septic tank brochure 2MB .pdf
Infiltrator TW series septic tank installation manual 570KB .pdf
Guide to installing tanks in high groundwater areas 3.4MB .pdf
Infiltrator TW series 1250 gallon tank specifications 868KB .pdf
Infiltrator TW series 1500 gallon tank specifications 746KB .pdf
and on YouTube is Infiltrator's 7-1/2 minute Setic Tank installation video

triple wall TW series Infiltrator septic tanks

Septic leach fields fail when poor septic tank design allows drain lines (laterals) to clog with sediment biomat forming. Greatly increase the life expectancy any sewage disposal system with a filter to prevent solids greater than 1/16th of an inch from entering and eventually clogging your leach field. Sieve filters extend beneath the scum layer (fats floating on top of tank water), siphoning relatively clear effluent from the middle. External-to-internal flow and sealed, gas-baffled end cap design prevents gas-borne solids (tiny particles) from floating atop gas bubbles and exiting. You will never need to replace this septic filter - just hose it off once a year, or less if everything seems constant the first time you check tank health. In normal usage, the filter schluffs debris, operating as nearly "self-cleaning" as possible. Septic tank fitting & filter kit (all 4" diameter sewer/drain SDR35) includes: a threaded cleanout, inlet and outlet beveled pipes, rubber seal grommets, hole saw kit, inlet tee, outlet tee housing, three spare couplers, and a sieve filter with handle extension kit (fits 4" SCH40 and SDR35 pipe). Please note the filter housing is ABS plastic, so use a multi-plastic cement when attaching to PVC outlet pipe. Always prime all glue pipe joints first, before cementing. Every installation tends to be unique, so we also include a hole saw kit that allows you to put the inlet, outlet, and inspection holes right where you need them. Trying to cut a round hole by hand or with a jigsaw can be a challenge, at best... risking ruin of the tank.

Septic sieve filter specification page

Another very important design consideration is having manhole risers above both compartments of the septic tank. When the time comes to have the tank pumped or spray off the filter, you need to have a riser above the opening. Otherwise, when you remove the lid, dirt and gravel will fall down into the tank. Manhole risers on a septic tank make life a lot easier. You really do not need, or want, to run your risers all the way to the surface - a foot of soil cover will allow grass to grow and provide insulation. More than a foot of soil atop the lids is not desirable since it forces too much weight/stress onto top of tank. And don't forget the threaded cleanout - the closer to house, the better (five feet should be considered a maximum distance). Another key design consideration shown here is keeping the septic tank no more than ten feet away from the foundation. You do not want to give grease and fats time to congeal in the line. Placing the septic tank farther than ten feet away from the house is often a critical error as is not venting your system as much as possible. Cleanout and diverter valve risers (along with leach field vents) should be terminated at least eight inches above grade, capped, and sides drilled with 1/16 to 1/8 inch holes. These holes drilled in sides of pipe extending above ground provide much need ventilation for tank and leach field alike.

typical septic tank and Infiltrator leach field installation

In most of the country, local regulatory officials allow homeowner-builders to submit a site plan and pull their own installation permits. Save money by renting a backhoe and installing your own septic system! Stamped, engineered, septic system plans are typically not necessary unless your property percolation test was extreme (greater than 60 minutes per inch or less than 5 minutes per inch); or the site has seasonal groundwater; or there is bedrock or unsuitable soil less than four feet below the proposed leach field; or if the ground slope is in excess of 30%  in the area of the proposed leach field. Engineered systems require a local professional engineer to approve (stamp) your site's septic tank and leach field plans. Anyone can draw up their own septic system plan, but legal liability then lies exclusively with your regulatory officials and they often defer to a licensed and insured local engineer. This releases the local government from future legal liability for your extreme septic system's failure. What is code in my area? is a uniquely local question and often changes yearly and varies from county to county in some states, so you need to check and see what is required on your property. Please note that we are not an engineering firm and we do not supply stamped, engineered plans, but we do consult for no charge with purchase of any complete septic system. Even professionals with 30 years in the business can get too tied up in 'how we've always done it' to realize simple improvements can make a huge difference in system performance and longevity. What follows is a very general guide to the average Individual Sewage Disposal System ISDS guidelines (code) in most of the country.

Do-it-yourself Infiltrator chamber leach field sewage disposal systems.

»   When you apply for your building permit, the local health department official will most likely help you design the sewage disposal system and may even offer to have their office perform a soil test (LTAR) in lieu of a percolation test. This involves digging a soil profile hole which is generally an eight foot deep trench in the area of the leach field. Most building departments wisely require a visual confirmation that there are no problematic soil conditions, groundwater, or bedrock in the area where you intend to put the leach field. But check with your local officials, as you may only need to provide a site plan survey (ILC) of your property (to establish setbacks from buildings, wells, streams, and property lines) and fill out some forms.
»   Your septic system site plan is typically drawn right on top of your property survey showing the septic tank 'setbacks' with tank 5-10 feet from the house, the leach field at least 20 feet from the house, at least 100 feet away from wells and streams, 25 feet away from dry gulches, and 10 feet away from the property lines. Or whatever the local regulatory officials require, so always check with the county first for minimum setbacks.
»   The home's sewer line drain pipe needs to slope 1/4 inch per foot downhill to the inlet side of the septic tank and the outlet pipe needs to flow downhill at least 1/8 inch per foot downhill to the leach field, where the septic tank effluent enters a manifold or distribution D box. Beyond the manifold or D box the leach field trenches (for an Infiltrator chamber system) are excavated perfectly level at a depth of at least seven inches below the grade of the manifold pipes or D box (for chambers). And covered with at least one foot of soil atop the trench or chamber. Trenches can be deeper, if the site dictates, but rarely more than three feet below finish grade.
»   If the leach field is uphill from the septic tank (or if the local health regulations simply require it) a lift station is installed in-line after the septic tank. An electric pump in the lift station tank forces effluent out to the leach field every time it fills to a certain level ("dosing"). Most ISDS codes allow field size reductions with dosing or automatic siphons, so there may be a certain advantage to installing a lift station when building on small lots and/or with nearby streams or ponds.
»   Never grind up (macerate) your sewage before sending to a septic tank unless absolutely necessary.   Pumping treated sewage (after septic tank) up to the leach field with lift station is always an option, but do not macerate (pump) effluent prior to the septic tank. The septic tank operates by digesting solids and settling sludge to the bottom and allowing grease to float to the top of the septic tank. Macerating the sewage before entering the septic tank will create a septic tank without any large solids, just a cloud of ground up sewage particles. When you send these particles out to the leach field, you are bound to eventually clog the soil with bio-mat and then the leach field fails.
»   Never use bleach, drain cleaner, or harsh soaps with a septic system. Bleach and detergents kill the helpful bacteria that thrives in a healthy septic tank to optimally process toilet waste. Lack of proper septic tank bacteria will cause your leach field to fail from excessive bio-mat accumulation.
»   Please... Never use ANY of those septic tank or leach field chemical additives and miracle enzyme cures. Supposedly breaking down fats and solids in the septic tank, in practice, these additives simply allow smaller particulates to pass through the septic filter (hopefully you have one) where they re-unite in the leach field forming a dense bio-mat. At best, they will do no harm to your septic system or the environment, just waste your money. The FDA does not approve of any of them - none of these septic cleaning and/or maintenance products have been proven effective in the long run. The deciding factor should be to ask yourself if you would like to see these additives find their way into your well water. Anything that can supposedly digest raw sewage should scare a person to have in their drinking water and thus their digestive system. A properly designed septic tank (two compartments and large enough) is going to operate just fine without of those over-hyped additives.
»   If your system is too large or not used enough, the septic tank can be subject to possible freezing in the winter. Steps must be taken to ensure good operation. Not pumping the tank right before winter is a good example: there is very little biological activity (bacteria consuming organics) to keep a clean sewage tank water warm. Always install waterproofing above septic tank to divert water and thus frost at least three feet away. In practice, this amounts to backfilling up to top of tank, sloping the ground away (mound) around perimeter, and then laying down a plastic tarp. If you can keep the water away from the sides of the tank, you can retain more heat in the dry ground and help speed decomposition of waste. A good tip is to set down a layer of straw before the tarp - it will cushion against rock damage and provide insulation. In extreme climates, a layer of two inch thick extruded polystyrene (EPS) foamboard insulation is recommended below the tarp.
»   If allowed, always divert greywater to a separate leach field (see greywater.html for details).   Greywater contains soaps, which are designed to kill bacteria (clean and disinfect things). You want to encourage helpful "good" bacteria (digesting anaerobic cultures) to grow in your septic tank, not kill them with soap laden graywater. If you cannot divert all of your greywater, just diverting the washing machine discharge will make a big difference in performance and eliminate a large portion of a home's effluent, taking the load off your leach field.


Check both compartments yearly and pump before enough solids accumulate in first compartment to spill over into second compartment. Usually less than sixteen inches - consult manufacturer of your tank.
Wrap a piece of white towel around the end of a long pole to check solids level in bottom of your septic tank. A healthy, properly sized septic tank might never need pumped, but not pumping when needed will result in grease and solids getting out to the leach field. Particulates, grease and solids create 'biomat' in the leach field percolation area, eventually causing it to fail and need replacement. Every three to five years is the normal cycle for pumping a septic tank (less often in warmer areas and/or lower usages). Should you live in an extremely cold climate, never have your tank pumped in the fall or winter - only pump in the spring. Septic tank water only avoids freezing through biological/bacterial activity (fecal matter decomposing).
Refill your septic tank with water immediately after having it pumped !!!
Without water on the inside, an empty septic tank is under extreme stress resisting the weight of backfill around it. This is especially true when soil is wet and when tanks are not properly bedded in plenty of gravel (selective, draining backfill). Stress is critical when sewage pumpers park too close to the tank, so always keep their truck at least 20 feet away. With enough stress, an empty concrete and fiberglass tank will crack, start leaking and eventually have to be replaced.
Install an effluent septic filter and spray it off during yearly inspection of tank
Sieve filters keep larger particles from getting out of the tank and compromising the leach field by clogging soil pores and causing failure (bio-mat). Septic filters are cheap insurance, installing easily in the second compartment of your septic tank.

Every septic system (except the cesspool) has two distinct components: Septic Tank to catch solids and Leach Field to dispose of liquid. Cesspools allow direct discharge of sewage (solids and liquid) into a pit, pond or perforated tank where effluent evaporates and leaches down into surrounding soil while solids remain behind. Septic tanks use one of seven treatment area designs to dispose of effluent:

Leach Pits are large gravel filled holes, optimally with a perforated tank in center for discharging effluent. Drywells are a passive (no pump) solution for small/odd lots where a long leach field percolation field is not possible or desired. Leach pits take advantage of surface area around sides of the hole to dispose of large amounts of water in the right soil types. Adding a drywell to a leach pit gives it additional capability to accept large surges at one time. Always allow at least eight or ten feet of undisturbed soil space between pits to ensure maximum percolation and effluent treatment.
Leach Fields are trenches (or rectangular beds) dug in yard and filled with a foot of 3/4" - 1-1/2" gravel and a four inch diameter perforated pipe. The pipe-in-gravel leach line is covered with geotextile fabric (landscaping weed barrier) and then backfilled with a foot or two of native soil atop. Gravity sends effluent to leach field with at least a 1/8 inch per foot drop and then is dispersed into soil evenly with all of the leach field perforated pipe being at the same level.
Chamber Systems are a tried and true advancement in leach field design - arched panels in the trench. Effluent flows into this large open area underneath the yard; the entire bottom of a chamber is open. With no gravel inside, chambers have ample air to help keep the leach field soil aerobic and healthy.
Pressurized Mound Systems make use of an electric pump to force effluent into elevated mound 'constructed soil' systems and distant trenches, beds or chambers. Even distribution of effluent is key to smaller leach field sizing and better treatment of the waste water. Poor soil percolation sites often require pressure distribution constructed sand mounds with two inch diameter pipe drilled with 1/4 inch holes every two feet, or so.
Evapotranspiration / Drip Beds are pressurized systems with smaller holes or nozzles (drip) for even more uniform distribution of waste water, but are prone to plugging from calcification of the nozzles. In areas that do not get snow cover in the winter, long shallow trenches can be run through yard, sending waste water into the root zone near surface. The plants transpire water through growth and some water evaporates being so close to surface, with a smaller portion of effluent percolating down into water table.
Lagoons, Cesspits, and Cesspools are man-made ponds where the effluent percolates and evaporates, often assisted by a fountain or bubbler. Normally reserved for high clay soil areas where percolation is difficult, lagoons can be lined to prevent percolation in a fragile area - evaporation being the only means of disposal. Six foot fencing and a locked gate are standard practice with any lagoon or cesspool due to the legal liability from safety issues.
Constructed Water Treatment Wetlands are shallow lagoons and mainly designed in hot climates since plant life is key. Active plant growth year-round is desired for the constructed wetland plants to help dissipate the nitrogen and truly treat the effluent. Constructed wetlands show the most promise for a carefree low-maintenance treatment area, but you do generally need to live in a non-freezing climate. They are an excellent choice for greywater disposal, taking a major load off the septic tank and leach field system (blackwater only - toilets and dishwasher).

Flow directors for use in septic system leach fields

One of the keys to a quality gravity distribution system is the flow director. Even distribution is VERY important to soil health in a septic system, so don't trust old-fashioned distribution boxes ("D Boxes") which are notoriously unreliable. Even a minor amount of settling will drastically affect a D box's even distribution. One of the most common mistakes with leach fields is relying upon simple Tees or Double Ells to properly distribute your effluent. Be aware of the fact that tilts as little as 1/8 of inch will result in enormous differences in effluent distribution with Tees and Ells.

Laboratory tests have shown that even at a 1/8 inch tilt, these flow directors deliver relatively equal flows (+/- < 1.3%). They are constructed of high quality PVC and easily install by attaching directly to 4 inch SCH40 pipe. We supply one flow director with each kit, but you can purchase additional units ($79 each) and install them in series to evenly distribute effluent to multiple lines.

Flow directors for use in septic system leach fields
Flow directors for use in septic system leach fields

This unique design allows monitoring of the effluent from grade, but the most important feature of our flow director is that it can be adjusted to either split the flow evenly between the two outlet lines OR alternate the flow to one side or the other. This allows you to let one half of your leach field go fallow for replanting and/or prevent hydraulic overloading. Unlike the large catalog companies we've experimented, installed, and serviced many system configurations over the years. We have the practical experience necessary to ensure your success.

Director Valves split 50/50 or all to one side for $69*
If you do not need any consultation, we offer the director separate
complete with threaded access cap, coupler for riser pipe, and flow adjustment handle
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