Septic Tank Risers

Definition, Need, & Installation of septic tank risers & access ports

What is a Septic Tank Riser

Definition: Septic tank "risers" are large diameter enclosures placed over the septic tank access covers to permit easy septic tank inspection and cleaning without having to "dig up" the septic tank at each occasion.

A septic tank riser consists of a bottom seal against the septic tank, a round large diameter material made of concrete, PVC (polyvinyl chloride), polyethylene, or occasionally steel that forms a "well" around the septic tank cleanout, and a cover that can be secured at ground level.

Typical septic tank riser diameter is 24-inches but 30-inch, 16-inch and other riser diameters are available. Risers are sold in varying heights from 6" and up.

Watch out: Occasionally, as you'll see in photos here, septic tank risers are made of other materials such as stacked concrete blocks or even wood. Generally these are unreliable and often they're very unsafe.

I was told my septic system needs a riser. What's that?

I was told that my septic system needs a riser. What is that and what does it look like? (May 14, 2011) Charles

Reply: definition & description of septic tank riser

A septic tank riser is simply a large diameter round pipe, typically a couple of feet across, that is placed over the septic tank cleanout opening to extend that opening up to close to the ground surface so that the septic pumping company does not have to dig deep into the soil in order to reach the septic tank cleanout cover for pumping and cleaning the tank.

Watch out: just as a septic tank must have a save and secure and childproof cover, so must a septic tank riser, cesspool, drywell, etc. Boys will be boys, as my grandsons demonstrate, standing atop a septic tank riser cover in Seal Isle City, New Jersey.

The Gilligan boys provide ample testing of the security and curiosity-proofing necessary at site hazards including septic tanks.

Shown below: an easy-to-access septic tank riser at a property we inspected in Norway.

Indeed we've seen septic tanks partially above ground, and others buried more than six feet deep.

It's not necessarily a mistake, and deep septic components may be required by site conditions, but the next section of this article give some considerations when the septic tank is more than a foot below ground surface

Septic Tank Riser Requirements & Dimensions

Septic risers are large-diameter "wells" that are placed over a septic tank inlet baffle access port (and possibly outlet) to permit easy access for septic tank pumping, inspection, and baffle repair.

Maximum septic tank depth before a riser is needed

If the septic tank happens to be buried more than just a few inches below ground surface, good practice includes (and sanitary or plumbing codes in some areas requires) installing a septic riser, a large diameter pipe that gives good access to the septic tank for inspection and cleaning.

Some building codes specify that a septic tank riser shall be installed if there is more than 6" of cover over the septic tank. - PIMA County AZ septic tank code

Minimum septic tank riser diameter

As we detail below, a septic tank riser enclosure must be of larger diameter when the tank is deeper in the soil. Otherwise it is simply not possible for a septic tank cleaning contractor to remove all or even most of the floating scum and settled sludge from the septic tank.

Our illustrations show the septic tank cleaning contractor using a muck rake - essentially a long-handled hoe-like instrument, to break up settled sludge and floating scum so that it can then be pumped out. If the tank opening is deep and narrow there is simply not enough room to perform this job properly.

The result of a too-small septic tank cleaning access opening is that much if not most of the solid waste is simply left in the septic tank, completely defeating the purpose of cleaning the tank in the first place.

Details of a proper septic tank cleanout are

at PUMPING the SEPTIC TANK

Septic tank riser diameter and height

Pre-fabricated concrete, plastic, or steel septic tank risers are typically sold in diameters of 18" to 36" and in heights ranging from 6" to 36" .

The septic tank riser must be at least as large in diameter as the septic tank inspection or cleanout port itself, and must be larger than the septic tank cleanout opening depending on the septic tank depth below the surrounding ground surface.

Here's a typical septic tank riser code specification

Septic tanks must be installed with at least one watertight riser extending to the ground surface or above.

The riser must have a minimum diameter of 20 inches when the soil cover above the tank does not exceed 36 inches.

The riser must have a minimum diameter of 30 inches when the soil cover above the tank exceeds 36 inches or when the tank capacity exceeds 3,000 gallons.

A gasketed cover must be provided and securely fastened or weighted to prevent unauthorized access. (Clackmas 2019)

Septic tank risers shall extend from the top surface of the septic tank to no more than six inches below the ground. - (Texas §§285.30 - 285.39 2012 & others)

This is in essence a requirement that no more than 6" of soil cover is used to bury the septic tank riser top if it is not in fact brought to or above the ground surface.

• A large diameter riser is 24" or more in diameter.
• Watch out: Small septic pumping risers that are just 4" or 6" in diameter are easy to install and cheap, but they do not permit inspection of the tank baffles, and their small diameter makes it difficult for the septic pumper to actually clean out the floating scum layer and sludge layer when the tank is pumped.
• Maximum septic tank riser height (or depth): 42" - 54"
  
  Septic tank risers are sold as stackable units with a minimum height above the septic tank (or soil depth) sufficient to bring the top of the riser level with or above the surface of surrounding soils.
  
  The riser height will be at least 6" (otherwise a riser isn't necessary) and could be 30 inches or more.
  
  Multiple septic tank risers must be mechanically fastened together and sealed against leakage, typically using stainless steel sheet metal screws and a nitrile gasket.
  
  The maximum septic tank riser height is determined by the maximum allowable septic tank depth, measured from the surface of finished grade to the top surface of of the septic tank, plus any requirement that the riser height extend above finished grade.
  
  Typical maximum septic tank depth (finished-grade surface to tank top surface) is 48" (four feet).
  
  So the maximum septic tank riser height (or depth) would be about the same - 48", plus an additional height if the installer brings the riser above surrounding grade.
  
  A reasonable maximum septic tank riser height (or depth) then would be
  
  54" if the riser extends 6" above surrounding grade
  
  48" if the riser extends to the finished grade or level of surrounding soil
  
  42" if the riser is to be buried to a maximum depth of 6" below finished soil grade level.
• Septic tank riser must be water tight
  
  Otherwise surface runoff or groundwater can and probably will leak into the septic tank, flooding and flooding the drainfield, preventing proper septic tank and drainfield function and leading to early septic system failure.
  
  Here is a typical septic tank riser water-tight code specification:
  
  After installation, all tanks must be watertight. The installer must test each tank for water tightness by filling the tank to a point at least 2 inches above the point of riser connection to the top of the tank. During the test there may be no more than one gallon of leakage over a 24 hour period. (Clackmas 2019)
  
• Septic tank riser lid: must be secure (for child safety) and water tight.
  
  "Secure" means that the septic tank riser cover is padlocked or requires tools to be removed or weighs at least 65 pounds, or has another approved means of securing the lid in place.

Steps in Adding or Installing a Septic Tank Riser

Illustration: a TuffTite Septic Tank riser, cited below.

PVC or poly septic tank risers will typically include the

septic tank riser itself, or multiple risers depending on the depth of the septic tank below the ground surface

an adapter ring that is bonded and sealed to the concrete septic tank top or existing concrete riser using a butyl rope or other sealant recommended by the manufacturer,

a riser lid that screws in place

How to Install a Septic Tank Riser

• Watch out: do not work alone. Leaning over or falling into a septic tank is usually quickly fatal. Protect the work area and keep onlookers at a safe distance during work on any septic system.
• Dig down
  
  to expose the septic tank cleanout cover - this may be at the inlet and outlet ends of the tank or more often over the center of the septic tank.
• Measure the depth
  
  from septic tank cover-surface to ground level and add a few inches to give the total septic tank riser height that will be required. You may need to purchase more than one septic tank riser to assemble the necessary height.
• Remove the existing septic tank cleanout opening cover
• Clean the septic tank top
  
  around the area where the adapter ring (for a PVC riser) or concrete or steel riser bottom edge (for concrete or steel septic tank risers) will contact the septic tank cover
  
  
  This means that the septic tank surface including mud and debris needs to be cleaned off and dry; installers use epoxy or other suitable sealants. Use alcohol or lacquer thinner to remove any water as well as grease or other contaminants and let the area dry thoroughly.

• Install the sealant
  
  such as butyl rope or other sealant specified by the manufacturer.
  
  Aerostream specifies use of a butyl rope sealant (shown here). PVC risers are usually sealed by using a butyl rope that is applied both to the bottom of the riser and to the adapter ring before it's screwed down. Orenco specifies a methyl methacrylate (MMA) adhesive sealant.
  
  (MMA is a combination resin+hardener two-component adhesive sealant that has good bonding properties and good temperature tolerance.)
  
  and if-used,
  
  Install the PVC adapter ring,
  
  sealing it to the septic tank lid (now clean and dry) to which the PVC septic tank riser will be installed.
  
• Set the riser in place: Place the round septic "riser" over the septic tank cleanout opening after first placing the rubber gasket or butyl rope or other sealant specified by the manufacturer. The riser may be bonded, glued, screwed in place, depending on the product involved.
  
  Some septic tank risers such as Tuff-Tite risers are secured to the adapter ring using special Robertson (square drive) screws.
  
  The diameter of the riser will have to be big enough that it is outside the perimeter of the septic tank opening (else it would fall in) and it will have to be tall enough to reach ground level or a few inches below ground level if you don't want it sticking up in view.
• Seal the bottom edge of the septic tank riser
  
  to the surface of the septic tank if additional sealant is needed for steel or concrete septic tank risers
  
  It's always good practice to be sure the riser is properly sealed: site conditions and weather vary.
• Seal riser sections
  
  between risers if multiple riser sections are required; that seal again depends on the riser material (concrete, PVC, steel); concrete, steel and some PVC septic tank riser sections can be sealed by an external wrap or by rubber gaskets between sections.
• Test the riser for leaks
  
  at or around the riser base: some manufacturers such as Orenco (see below) describe a test procedure that requires filling the septic tank to 2-inches above the base of the riser to inspect for leakage. This will of course require temporary plugging of the septic tank inlet and outlet openings.
  
  Orenco recommends following the tank manufacturer's instructions or watching for at least 30 minutes for leaks at Orenco's fiberglass tank risers. The water level in the riser should not drop during the test period and no water leaks or even droplets should be visible on the exterior of the riser base.
  
  Watch out: this is an important detail since leaks around the riser base can send groundwater or surface runoff into the septic system, flooding it and causing costly damage to the drainfield
• Install the riser cover:
  
  Place a secure and safe cover over the top of the septic tank riser
• Backfill
  
  soil around the riser so that things look nice again.
• Watch out: for safety and to prevent children from possibly opening and falling into the septic tank, install a safety lock or combination lock on the riser lid if it's a lightweight one that could be lifted by one person.

Watch Out: Deep drainfields mean poor septic effluent processing. If a deep septic tank means that the absorption area (leach field or drainfield are synonyms) is deep, such that the top of the soil trenches are more than a foot below ground surface, then the reduction in aerobic bacteria in the soil will limit the effectiveness of the drainfield in reducing pathogens and other environmental contaminants.

Additional septic effluent treatment methods can correct these conditions, but it's useful to keep in mind that there is a difference between successful septic effluent disposal and successful septic effluent treatment. A deep septic tank does not necessarily mean that the absorption area is also deep, since site conditions and use of septic effluent pumps may change the required depth of a drainfield.

Watch Out: Be sure that the septic tank riser and all septic tank covers are sound and secure since falling into a septic tank can be fatal.

See SEPTIC & CESSPOOL SAFETY .

The two septic tank access risers shown here are dangerous and could easily involve a fatality. At below left is a collapsing home made septic tank made of concrete blocks over which someone placed a concrete cover and slabs of slate to try to cover this dangerous hazard - an inadequate response.

At below right was a two-concrete-block high septic tank riser provided at a mobile home park in New York. The site manager had simply left the septic tank cover off.

Septic Tank Riser Installation Instructions

• AERO-STREAM SEPTIC TANK RISER INSTRUCTIONS [PDF] AS-113 and other models, Aero-Stream®, LLC W300N7706 Christine Lane Hartland, WI 53029 USA, Tel: (877) 254-7093 TOLL FREE (262) 538-4000 Local (262) 538-4093 Fax info@aero-stream.com retrieved 2019/08/27 original source: https://www.aero-stream.com/wp-content/uploads/I-Sheet-AS-Riser-Kit-102368-Rev-F-current-1.pdf
  
  Watch out: installation instructions excerpt from AeroStream:
  
  CRITICAL SAFETY WARNING: Always securely attach Riser Cover to Riser by installing and tightening the (4) screws using the appropriate driver tool. Cover security must be checked after each tank servicing.
  
  Cover must be inspected regularly for damage and security. The secondary safety barrier must be securely fastened in place at all times.
  
  The safety barrier must only be removed to gain entry into the tank by a properly credentialed professional donning appropriate safety gear. An unsecured cover or secondary safety barrier is a serious safety risk.
• AFS, Automated Flow Systems Septic Tank Risers, Kor-Flo™ 30" diameter PVC septic tank risers are made of ribbed PVC pipe that are similar in appearance to the Orenco risers shown here. Contact: R.C. Worst Co., R.C. Worst & Company Inc. 625 E. Best Avenue Coeur d'Alene, Idaho 83814 USA Tel: 855.329.4519 Offices also in Spokane and Idaho Falls.
• Butyl sealant rope is produced by 3M, Poweka, XFasten and other manufacturers. Septic tank riser providers will specify and will provide an appropriate sealant formulated for their riser products.
• Clawson, Beth, MSU BENEFITS of SEPTIC TANK RISERS [PDF], Michigan State University Extension, Water Quality, (2018) retrieved 2019/08/27 original source: https://www.canr.msu.edu/news/the-benefits-of-septic-tank-risers
• Clackmas County SEPTIC SYSTEM RECOMMENDED STANDARDS AND GUIDELINES [PDF] (2019) (OAR 340-071-0220) Clackmas County, Oregon. (Clackmas COunty is part of the Portland-Vancouver-Hillsboro OR-WA metropolitan area in the Wilamette Valley. The county seat is in Oregon City. - retrieved 2022/08/11
• DelZotto Septic Tank Risers, Delzotto, 4575 West Highway 40, Ocala , Florida 34482 USA Tel: (866) 487-2139 Website: https://delzottoproducts.com
• EZSet™ Septic Tank Lids & Risers, Infiltrator Water Technologies, sold in 20", 24" and 30" diameter, glass reinforced polypropylene septic tank risers & lids, green or black, used with concrete or plastic septic tanks. Lids secured with stainless steel screws. Contact: Infiltrator Water Technologies 4 Business Park Road P.O. Box 768 Old Saybrook, CT 06475 USA 800-221-4436
  
  Website excerpt: EZset™ Lids & Risers EZset™ Lids & Risers Logo EZset™ risers and lids by Infiltrator are made from glass reinforced polypropylene, providing superior strength and durability.
  
  They come in green or black and in 20”, 24”, and 30” diameters, making them ideal for use with any concrete or plastic tank. The slip resistant lids are fastened using stainless steel screws and can be further secured by installing locking rings.
• MINNESOTA, UMN, SEPTIC TANKS DEFINITION & DESCRIPTION [PDF] University of Minnesota, - retrieved 2022/08/11 original source: https://septic.umn.edu/sites/septic.umn.edu/files/section_7_2017.pdf
• North Carolina, SEPTIC/PUMP TANK RISER ASSEMBLY CONDITIONAL APPROVAL [PDF] (2004) for Polylok septic tank risers, North Carolina Department of Environment and Natural Resources
• ORENCO PVC SEPTIC TANK RISER INSTALLATION INSTRUCTIONS [PDF] (2017), Orenco Systems®, Inc., 814 Airway Ave., Sutherlin, OR 97479 USA Tel: 800-348-9843 / 541-459-4449 Website: www.orenco.com retrieved 2019/08/27 original source: https://www.rcworst.com/Shared/content/mfr/orenco_systems_inc/docs/orencorisertainstallins_nin_rla_rr_1_prn.pdf
  
  These PVC septic tank risers are installed on concrete septic tanks using a sealant, adhesive (methacrylate) and riser set into an adapter channel cast into the septic tank top.
• ORENCO SYSTEMS AX-RT TREATMENT UNIT INSTALLATION MANUAL [PDF] page 10 discusses riser installation, Orenco Septic Tank Risers & Lids
• PIMA COUNTY PDEQ SEPTIC INSPECTION for CHAMBER SEPTIC SYSTEMS [PDF]
• POLYLOK SEPTIC TANK RISER INSTALLATION INSTRUCITONS [PDF] Polylok Inc., Zabel, Polylok Inc. 3 Fairfield Blvd Wallingford, CT 06492 USA Website: www.polylok.com, Tel: 1-877-765-9565 retrieved 20189/08/27 original source: https://www.polylok.com/sites/default/files/Riser_Installation_2.pdf
• TEXAS, SUBCHAPTER D: PLANNING, CONSTRUCTION, AND INSTALLATION STANDARDS FOR OSSFS §§285.30 - 285.39 [PDF] (2012), Texas Commission on Environmental Quality, retrieved 2022/08/11, original source: https://www.tceq.texas.gov/assets/public/legal/rules/rules/pdflib/285d.pdf
• Thurston County WA SEPTIC TANK MANHOLE RISER INSTALLATION PROCEDURE [PDF] Thurston County Washington Department of Health, Thurston County Courthouse Complex 2000 Lakeridge Dr. SW Olympia, WA 98502 Information Desk: (360) 754-3800 Telecommunications Device (TDD): 711 or 1-800-833-6388 retrieved 2019/08/27 original source: https://www.co.thurston.wa.us/health/ehoss/pdf/RiserInstall.pdf
• TUFF-TITE SEPTIC TANK RISER & LID INSTALLATION INSTRUCTIONS [PDF], Newmarket Pre-Cast Concrete Products Ltd. 20 Victoria Street North PO Box 1179, Uxbridge, Ontario L9P 1N4 Phone: 905.852.6111, Fax: 905.852.4340 Toll Free: 1.800.263.1297 Website: www.newmarketprecast.com Email: info@newmarketprecast.com retrieved 2019/08/27 original source: https://www.newmarketprecast.com/public/product_document/14423182945_How%20to%20Install%20Tuftite%20risers.pdf
• UTAH ADMINISTRATIVE CODE 317-4-6 SECTION R317-4-6 - SEPTIC SYSTEM DESIGN REQUIREMENTS [PDF] (2022) Utah State Regulations, retrieved 2022/08/11
• US EPA, HANDBOOK FOR MANAGING ONSITE AND CLUSTERED (DECENTRALIZED) WASTEWATER TREATMENT SYSTEMS [PDF] https://www.epa.gov/sites/production/files/2015-06/documents/onsite_handbook.pdf
• ZOELLER PUMP CO. SEPTIC TANK RISERS [PDF] (2008) product data sheet, 12", 24" & 30" riser diameters, UV-Stabilized fiberglass cover, PVC risers are rated for 2500 pound wheel loading. Zoeller Pump Co., P.O. BOX 16347 • Louisville, KY 40256-0347 USA, Website: www.zoeller.com, Tel: (502) 778-2731 • 1 (800) 928-PUMP • FAX (502) 774-3624