How to Build a Septic Tank

Building and constructing a large septic system yourself can result in a costly and smelly mess to clean up if not done properly. Since government and health officials are largely involved in the building of a septic system for a home of three or more, undertaking a project of that magnitude on your own is not advisable. This article will guide you through building your own private septic tank for a maximum of two users.

Required Materials

  • 9 cubic yards of ¾ or 1 ½ inch crushed rock
  • 80 square feet of landscape fabric
  • 2 55 gallon plastic drums
  • 10 feet of 4” ABS plastic pipe
  • 1 4” ABS 90 degree bend (or street Ell)
  • 1 4” ABS Y branch (or Y Bend)
  • 3 4” ABS 45 degree bend
  • 4 10 feet length of 4” perforated drain pipe
  • 2 4” drain pipe couplers
  • 2 4” toilet flanges
  • 1 4” level
  • 10 wood stakes
  • 1 set of PVC stakes
  • 1 set of PVC glue
  • 1 two part epoxy or silicon sealant
  • 1 1” thick wood block

Required Tools

  • 1 duct tape
  • Shovel
  • Saber Saw

Assembly instructions

  1. Assemble all supplies, parts and equipment listed before starting.
  2. Dig a ditch 4 feet wide, 26 feet long and 3 feet deep.
  3. Cut a hole in the top of each drum the size of the toilet flange pipe’s outside measurement with a saber saw (It should be near the edge).
  4. Attach 4” toilet flange to each hole.
  5. Cut two holes in the top side of the lower drum, 45 degrees away from a perpendicular line drawn from the hole on top to the far side.
  6. Cut one hole in the upper drum opposite the hole in the top.
  7. Place the drum with one hole in the side at the end of the trench.
  8. Level the drum so the top is at least 4 inches below grade.
  9. Dig a hole about 1 foot deeper for the placement of the second drum in front of the first.
  10. Dig the hole in step 9 a little deeper and fill with gravel until the 90 Ell fits perfectly from the hole in the side of the top drum to the toilet flange of the lower drum.
  11. Cut a 3 ½” piece of 4” ABS pipe (nipple) and glue it into one end of the 90 Ell. Cut another nipple about 2 ½” long and glue it in the other end.
  12. Test the fit for alignment between the two drums. Ensure the end with the short nipple goes into the upper drum.
  13. Glue the end of the 3 ½” nipples into the toilet flange.
  14. Glue a “Y” to 3 ½ nipples and add a 45 degree bend to the left side of the “Y.”
  15. Align the “Y” to meet the incoming waste line, and glue it into the toilet flange.
  16. Cut and glue two 2 ½” nipples to the remaining two 45 degree bends at one end only. Insert into the holes on the side of the lower drum. The face of the two 45 degree bends should be perpendicular to the trench.
  17. Pound a stake into the ground so that its top is level with the bottom of the 45 degree bend coming out of one side of the bottom drum.
  18. Tape a 1” wide block to the end of a 4 feet level.
  19. Start the second stake a little less than 4 feet down the trench from the first.
  20. Lay the end of the level without the block on the fist stake and the block on the second. Pound the stake down until the level shows even when the block is on the second stake. The second stake is now 1” lower than the first, or ¼” per foot.
  21. Repeat this process until you have stakes the length of the trench.
  22. Place gravel in trench until the top of the gravel is level with the top of the stakes.
  23. The gravel should now slope away from the drums at ¼” to the foot.
  24. Connect two pieces of 10 foot 4” perforated drain pipe with a slip coupler (holes down). Slide one end into the 45 degree bend of the lower drum. Repeat on the other side.
  25. Check the drain pipes with the level and block to see if the ¼” grade is consistent along the length of the pipe. Adjust by adding or subtracting gravel under the pipe.
  26. Seal the 45 and 90 degree bend to the lower and upper drums respectively, using a two part epoxy or silicon caulk.
  27. Bury the trench to the top of the bottom drum with the remaining gravel.
  28. Lay landscape fabric over the gravel to prevent the soil from seeping into it.
  29. Fill the remaining trench area with soil, compacting well to the original grade.
  30. Fill the upper drum with water.

Tips and Warnings

  • This septic tank system is not designed to accommodate the needs of a large household. It is best for a small travel trailer or RSV and two people maximum.
  • Depending on use, the upper drum may have to be pumped once per year.
  • Follow local Septic Regulations when constructing a septic system of any size.
  • Have the system inspected by the county before covering everything.
  • Do not place septic system too close to trees. Tree roots will grow in your line and cause them to clog. With time this will damage your system.
  • Find out if you need to buy a permit before beginning construction. This will avoid having to dig up the system later for inspection.

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How to Build a Septic Tank