Installing Access Risers

Caution Sewer GasSeptic Access with RisersFundamental septic system maintenance involves evaluating the status of your septic tank and pump chamber (if you have one), which can be time-consuming and labor-intensive without access ports known as risers. Imagine having to dig through two feet of dirt to check the oil in your car! Below is a four-step guideline for installing septic tank risers for an on-site septic system.

Please note that the current Washington State Code requires risers for all septic systems so you may be required to install them if you are applying for a building permit, land division, or any other governmental action.811 Call Before You Dig

A Few Safety Tips Before You Get Started

  • Hitting an underground power line while digging can be deadly! If you are at all unsure about underground lines on your property, have them located by calling 800-424-5555 or 811 or visit the 811Online website.
  • Use the buddy system! Fumes associated with exposed sewage can be harmful causing a person to become unconscious so always work with a partner.
  • Never leave an open septic tank unattended! Once the lids are off be careful around the tank and keep pets and children safely away.
  • Evaluate your septic tank's integrity! If a septic tank is 20 years old or older, it is advisable to pump the tank to verify its structural integrity and water-tightness. If the tank is in need of serious repairs, it is better to replace it with a modern septic tank that will include risers with the installation. Replacing a septic tank requires a permit from your local Environmental Health department.

Gather All the Materials & Tools You Will Need

Septic Riser GraphicMost of the materials needed to install septic tank risers should be available at your local plumbing hardware store or online. There are different types of PVC risers available. Some brand names you might recognize include "Tuf-Tite", Polylok and Orenco. Risers are normally 24 inches in diameter and can easily fit over the tank hole opening. Some tanks have square openings so fitting a round riser over the square opening can be tricky. Square plate adapters with round openings are now made for this purpose. Some types of risers are cut to order based on the height you need, and some come in 6 or 12-inch increments.

Note: You will need to measure the size of the hole in your septic tank. Then buy the Adapter and Risers slightly larger than the hole. For example, if the hole in your septic system is 22 inches across at its longest point you will need to purchase the 24-inch Tank Adapter Ring, 24-inch Risers, and 24-inch Lid. 

Parts of a Septic RiserTo install a riser system on your septic tank you will need the following parts:

  1. Tank Adapter Ring (TAR)
  2. Kit for Riser Adapter Rings
  3. Butyl Rope
  4. Risers
  5. Domed Lid or Flat Lid
  6. Stainless Steel Screws

Tools for Digging TankMaterials needed for digging up your septic tank(s):

  1. Septic System 'As-built' Record drawing
  2. Measuring tape
  3. Shovel
  4. Probing tool
  5. Eye protection
  6. Work gloves

Tools needed to cut risers to correct size:

  1. Saws (circular, saber/jig and hand)
  2. Drill with 1/4 inch bit
  3. Rasp or fileTools for Installing Risers
  4. Marking pen
  5. Tape measure

Materials needed to seal risers to the tank:

  1. High-strength concrete patch mix
  2. Small bucket
  3. Mixing stick
  4. Gloves

Easily install access risers on your septic components following the 4 simple steps below or print out a copy of the Septic Tank Manhole and Access Riser Installation Brochure (PDF) from Thurston County Environmental Health.

Step 1: Locate Your Septic Tank(s)

Single Access with RiserThe best way to find your buried septic tank(s) is to reference the 'As-built' Record Drawing associated with your septic system. This is a plot plan showing where your septic system was installed on your property and should include distances to septic components from landmarks. If you do not have an 'as-built' follow the instructions to locate septic-related documents using the Online Permit System. If an as-built is not available, you may want to contact Environmental Health to check the paper records or call a professional (PDF) to locate your tank.

Identify the location of your tank on the as-built. Using the probing tool, gently poke around the area of the septic tank until you hit concrete. Septic tanks may be buried 6 inches to 5 feet below ground.

Warning: Underground power or other utility pipes or cables could be near or over your septic tank, and if you hit a power line it could be deadly! Make sure you have any electrical utilities located before you begin digging by calling 800-424-5555 or 811 or visit the 811Online website.

Step 2: Uncover Your Septic Tank(s)

Once you have located your septic tank, begin digging.

The dimensions oUncovered Tankf the tank are normally about 6 feet wide by 8 feet long. Dig out the entire top of the tank and remove rocks and dirt around the lid openings. You will want to remove any dirt that is on the top of your septic tank. Doing so will help insure that you create a good seal. You should have two openings; one over the inlet (from the house) and one over the outlet (into the drainfield or pump chamber). Or you may have one large lid in the middle and one small lid on one or both ends. You will need a riser for each opening. Septic tank configurations can vary, so if your tank is completely different than these examples you may want to contact a professional. The inlet side is typically the one closest to the house.

Expose all manholes and the inlet and outlet baffle covers. It is helpful to uncover the entire top of the tank. This allows plenty of room to work and leaves an area to stack and bury in place the old concrete lids. To properly install risers, all manholes (holes that are 24 inches or larger or square) must be retrofitted and the tank inlet and outlet baffle covers (if separate from the manholes) must also be retrofitted.

Note: Septic tank risers are normally installed in pairs. If you find one - and only one - riser already installed then it is most likely for the pump chamber which only needs a single riser for accessing the pump. Look inside, if it is not a septic tank you should locate your septic tank and install risers for both the inlet and outlet openings, as described above.

Remove the concrete lids, when the job is complete they can be discarded, you will not need the concrete lids once risers are installed. If you have a conventional gravity system consult your 'As-built' Record drawing to determine if you have a distribution box (D-box) which you will also need to uncover and install a riser on.

Caution: NEVER leave an open tank unattended! Once the lids are off be careful around the tank. Make sure that pets and children are kept away from the tank while it is open, you don't want them falling into the tank. Let someone know where you are in case you have an accident. It is best to do the work with another person present. Be aware that exposure to sewage can cause serious illness, so make sure you wear gloves and wash up afterward with plenty of soap and water. You may also want to wear eye protection in case you get splashback from debris falling into a tank.

Step 3: Fit Risers to Component Openings

Depending on the diameter of the septic tank manholes, large risers will either sit on top of the septic tank or fit down into the tank opening 1 to 3 inches. Keep this in mind when determining the height of the riser. It is easy to trim off the extra - it is hard to add a few inches more!

Measure the diameter of the manhole cover:Riser Lid

  • If the opening is 26 to 29 inches, the riser will fit down into the tank opening. Measure the distance from ground to the top of the septic tank and add 3 inches.
  • If the opening is more than 29 inches: a 3-foot square fiberglass plate (with a 22-inch hole in the center) is needed. It sits over the manhole and reduces the opening so that a 24-inch riser can be used instead of a more expensive 30-inch riser.

Measure the distance from the ground to the top of the fiberglass plate. You may wish to install the risers so that they are flush with the surface of the ground or sticking out above ground by a few inches (if a riser is above ground make sure you are careful when mowing).

Riser RingHint: To shorten a large riser with ribs, drill a 1/4-inch hole between the ribs above the cut line and use the saber or jig saw to finish the cut by following one of the grooves between the ribs. File off any high spots, if needed. The large riser can be made to fit snugly into a smaller manhole opening by removing one of the ribs. Use a circular saw with the guard held open - plunge cutting around the riser until the rib is removed.

Step 4: Attach Risers to Septic Tank(s)

Riser SealCaution: If the septic tank is 20 years old or older, it is advisable to pump the tank to verify its structural integrity and water-tightness. If the tank needs serious repairs, it is better to replace it with a modern septic tank and include risers with the installation. Replacing a septic tank requires a permit from the local health department.

Clean off the top of the tank, removing all dirt and debris. Follow the manufacturers' instructions to assemble the risers components using the butyl rope. Then use a high-strength flexible concrete patch mix that hardens in 15 to 20 minutes to attach the riser to your septic tank. Some brand names include Jet-Set, Rapid-Set, Thorough-Set or Perco-Plug. Use heavy-duty leather gloves when handling these products and mix according to instructions.

Note: mix a small amount of concrete patch at a time for best results. The stuff hardens fast.

Seal the riser to the septic tank using the patch mix. You may finish sealing by adding Bentonite or casing sealer around the base, filling in gaps as needed.

Make sure you then carefully secure the riser lid with the screws provided to avoid a safety hazard! Woman Drilling Riser Lid

All risers must be completely sealed to the septic tank. Smaller risers for the inlet or outlet openings, if present, should have the bottom few inches sanded with rough sandpaper to facilitate a stronger bond. Holes and gaps between the riser and the tank are easily filled if the patch mix is mixed thick and held in place for a few minutes. The company where you purchase the risers and lids can also be a good source of information regarding proper installation of risers on septic tanks.

Of course, if you are unsure of doing this work yourself you may want to hire a professional to locate your system, install risers and lids, and perform any other needed maintenance.

Thank you to Thurston County Environmental Health for providing the basis of this documentation.