Most concrete septic tanks are installed with heavy concrete lids over the manholes and access holes and then covered with soil. While this is an adequate installation, many septic professionals recommend replacing the concrete lids with plastic risers and lids for better access when inspecting and cleaning the tank. By adding a riser, the new plastic lid is easily accessible for pumping and maintenance. The plastic lids are also bolted down, providing an extra level of safety for the homeowner and family.
Remove all the soil on top of the septic tank. Generally, the tank is between 1 and 3 feet below the surface of the soil.
Measure the diameter of the lids and any tank inlet or baffle outlet covers. If the larger lid, or "manhole" lid, is more than 24 inches in diameter, it may require an adapter before fitting the lid riser over the hole. Adapters are available from the lid riser manufacturer.
Remove the concrete lids and set it aside. Avoid breathing any fumes rising from the septic tank and wear a protective mask to reduce exposure.
Measure the distance between the tank and the ground. Trim the riser if necessary according to the manufacturer's directions. Usually, however, you need to drill a hole at the appropriate length for the riser. Then, using a jigsaw, trim off the excess riser length. Some manufacturers make adjustable risers, making trimming unnecessary.
Sand around the bases of the risers with a 40- to 60-grit sandpaper. Wipe it with a tack cloth, then place the risers over the manholes, and the intake and outlet holes.
Mix the recommended quick-drying, high-strength, flexible concrete patch mix in a bucket. Work quickly, the mix dries in 15 to 20 minutes. Apply liberally around the bases of the risers with a trowel, completely sealing the edges to the top of the septic tank. Allow to dry completely.
Bolt the lids onto the risers according to the manufacturer's directions, using a socket wrench.
Cover the septic tank with soil.