A septic tank is buried, and the openings you need to reach — the access ports over each compartment — are buried with it. A riser is a short vertical collar that sits on top of one of those openings and brings it up to ground level, finished with a removable lid that sits flush with your lawn.
That is the whole idea. The tank stays exactly where it is; the door to it moves up to where you can reach it. Most tanks need more than one, because most tanks have more than one opening: on a job in Redmond we fitted new 24-inch risers over both compartment lids and a 12-inch riser over the crossover baffle between them — three openings, three risers.
Without risers, every visit to your septic tank starts with a shovel. The lid has to be located and dug out before anything else can happen, and then backfilled afterwards — every pump-out, every inspection, every time. At a property in Roy the system had no risers and needed direct excavation for service. At a Bonney Lake tank sitting about two inches under the grass, our technician recorded that the lack of risers made future access and maintenance more difficult.
There is a worse version of this, and it is not hypothetical. On that same Bonney Lake visit the outlet access lid was stuck and could not be opened, so the outlet pipe could not be fully inspected. The tank was pumped, but part of the job simply could not be done that day. A buried lid that has been undisturbed for years is not guaranteed to open when someone finally needs it to.
Buried lids are also where roots get in. In Redmond the root intrusion we found was coming through the second compartment lid and the crossover baffle lid — not through the tank structure, which was sound. The seams sitting under soil were the way in.
Four reasons come up again and again, and only the first is about convenience.
Access to a septic tank is not purely a matter of preference in Washington. The design rules for on-site sewage systems are specific about it.
The digging is most of the job. The tank's access openings are excavated and exposed, the riser sections are set on the openings and sealed, and the lid is fitted at the new surface level. In Redmond that meant opening the first compartment lid, the second compartment lid and the crossover baffle, clearing out the root intrusion we found there, and then fitting the three risers.
Because the excavation is the expensive part, it is worth doing while the lids are already open — on the same visit as a pumping or an inspection rather than as a separate trip. That is also when the case for risers usually becomes obvious: on an inspection on Anderson Island we recorded that the tanks would benefit from proper risers, which would give easier access for future inspections, maintenance and pumping while removing the need for extensive excavation every time the system needs service.
If you are not sure whether your tank has risers, the quick test is whether you can see a lid. A circular cover flush with the ground is a riser. Grass with nothing on it is a tank you will be digging for.
A short vertical collar fitted over an access opening on a buried septic tank, bringing that opening up to ground level and finishing with a removable lid at the surface. The tank does not move; the access to it does.
One for each access opening, so usually more than one. A two-compartment tank typically has an opening over each compartment and often one over the crossover baffle between them. On a recent Redmond job that meant three: two 24-inch risers over the compartment lids and a 12-inch riser over the crossover.
For systems being designed and installed, WAC 246-272A-0238 requires service access at finished grade, with a narrow exception where a local health officer may allow a gravity system's tank access to sit up to six inches below grade if a marker is installed at finished grade. These are design requirements and are not applied retroactively, so an older buried tank is not in breach - but access rebuilt today is rebuilt to that standard.
Risers and riser lids fall under what the state rule calls a minor repair, and whether a permit is needed for a minor repair is decided by the local health officer rather than set statewide. It depends on your county, and we handle that as part of the job.
Yes - that is the usual case. Most riser installations are retrofits to tanks that were buried without them. The access openings are excavated, the riser is set and sealed on the opening, and the lid is fitted at ground level.
It is worth considering, because the excavation is the bulk of the work and the lids are already open during a pumping or inspection. Combining the two avoids paying to uncover the same tank twice.
A properly fitted and secured lid is the safe arrangement, and the state rule requires accesses to be secured to minimize injury or unauthorized access. A lid that is cracked, loose or missing is genuinely dangerous over an open tank and should be dealt with straight away rather than at the next service visit.
Our team recently completed a septic system excavation and inspection project for a homeowner in Redmond, WA after concerns about root intrusion inside the septic tank. The goal was to expose the tank, inspect its condition, eliminate the source of the root intrusion, and make future maintenance much easier. After arriving on site, we excavated […]
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