Septic tanks have one or two access openings with a riser above each. If there are two risers, one is positioned above the inlet baffle and the other at the outlet baffle. Plumbers use the risers to access the septic tank to check for clogs in the baffles. Septic tank pumping services use the risers to insert hoses to pump any sludge buildup from the tanks.
Septic tank depths vary, depending on the depth of the basement of the home. A home with a deep basement will have a septic tank where the top of the tank is below the level of the floor of the basement. The riser is long enough to reach between the top of the septic tank and ground level. Concrete and PVC are the most common riser materials.
The most convenient riser cover fits low over the riser pipe at near ground level. This allows you to mow over the riser cover rather than around the fixture.
The riser cover should fit tightly over the riser pipe to prevent rainwater and snow melt from entering the septic tank through the riser, which would increase the septic system load. Use a cover that latches in place or has another childproof security feature to prevent playing children from opening the riser and dropping items into the septic tank.