DIY Septic System Installation
- 1). Lay out the planned system. Measure and mark setbacks and spray paint the planned outline for the system. Dig a trench for a pipe connecting the building drain to the septic tank, a deeper space to accommodate the septic tank and trenches for the drainfield.
- 2). Prepare the site for the pipe connecting the house to the tank. The pipe, which typically must be at least 3 inches wide, should be resting on solid soil that will not compact further. Often, bedding sand must be added to the trench bottom and compacted. The trench should have a slight slope so that it decreases about 1/4 inch per foot between the house and the tank.
- 3). Install the pipe, starting at the house drain. Work in sections, checking the level of each segment of pipe and making adjustments before making watertight connections.
- 4). Prepare the hole for the tank and place the tank in the ground. Often, the tank provider will perform installation, which may include digging the hole. The depth that the tank is placed at should be dictated by the depth of the pipe draining wastewater from the house, as this should align with the inlet on the tank. Some jurisdictions may require that the tank be placed atop a bed of sand with a specified thickness.
- 5). Install an outlet filter or bioscreen in the tank according to the filter manufacturer's instructions.
- 6). Install inlet and outlet pipes. There should be at least 4 inches between the end of the pipe and the baffle. If the inlet pipe is too close to the baffle, it can cause a clog or backup. Some inlet and outlet holes have a neoprene collar that only has to be wet for the pipes to enter and seal, while other tanks have large holes, which must be sealed after the pipe is inserted using mortar, grout or mastic.
- 7). Backfill around and on top of the tank. Be aware that the tank may need to be inspected and risers placed on either end of the tank before being backfilled. Compact the backfill as it is placed around the tank to prevent later settling, and crown the fill over the tank so it is at least 6 inches above the tank.
- 8). Excavate the trenches for the drainfield. Only dig the trenches when soil is dry and crumbly. Local codes generally dictate the necessary depth, width, length and number of trenches. The trenches should be level.
- 9). Attach 4-inch, non-perforated sewer pipe, level "T" pipe and joints between the tank outlet pipe and the drainfield trenches as needed to connect the tank and field.
- 10
Place at least 12 inches of clean, silt-free gravel or stone aggregate, 3/4-inch to 2 1/2-inch in size, at the bottom of the trench. Use the laser level to make sure the aggregate in the trench is level and make adjustments as needed. - 11
Assemble the perforated PVC pipe that extends the length of the trench. The outlet holes should be aligned at 4 and 8 o'clock in relation to the trench bottom, not facing down or up. The end of the pipe in each trench should have a capped inspection port that will extend above ground level. - 12
Cover the pipes with at least 2 inches of washed gravel or stone. - 13
Cover the gravel with synthetic fabric filter or another suitable backfill barrier. - 14
Backfill the trenches and vegetate the drainfield with shallow-rooted plants. The distribution system may need to be inspected before the trenches can be filled in.
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