Is your septic tank frequently filling up? It’s a common issue, especially during Bali’s wet season. Understanding how a septic tank works and the correct sizing can save you from frequent pump-outs and potential health hazards. This guide will help you navigate septic tank problems, understand their design, and calculate the right size for your Bali property.

Why is My Septic Tank Always Full?

Several reasons could cause your septic tank to fill up faster than expected. Here’s a breakdown:

• Groundwater Intrusion: If your tank fills up rapidly during the wet season, groundwater is likely seeping into the tank. This can happen if drainage water is connected to the tank or surface water runs into it.
• Incorrect Pipework: Septic tanks should only receive waste from toilets, showers, washbasins, washing machines, and sinks. Drainage water should be kept separate.
• Poor Drainage: If the tank is located in an area with poor drainage, such as clay-lined areas, surrounding water may infiltrate it.
• Cracked Tank: While less common, a crack in the tank can also allow groundwater to enter.
• Blocked Outlet Pipe: A blocked outlet pipe can cause the tank to fill up because the semi-processed waste can’t drain properly.
• Blocked Internal Pipe: The pipe between the primary and secondary chambers could be blocked, causing the first chamber to overflow.

How Does a Septic Tank Work?

A typical septic tank has at least two chambers.

1. Primary Chamber: In the first chamber, solids settle to the bottom as sludge. Bacterial action begins to break down the sludge and wastewater. Scum from this process is trapped on the surface.
2. Secondary Chamber: Semi-processed waste flows to the second chamber via an internal pipe, where further bacterial action breaks down the wastewater.
3. Soak Field: The processed water then drains from the secondary chamber to a soak field.

Identifying the Cause of the Problem

Follow these steps to diagnose your septic tank issue:

1. Verify if the tank is actually full: A blocked pipe leading to the tank will cause backups in showers and toilets, even if the tank is not full.
2. Check for drainage and surface water: Ensure that no drainage or surface water is entering the tank, and that no pooling of water is occurring over the tank.
3. Inspect the outlet pipe: Check that the discharge pipe from the tank is clear and that it is lower than the inlet pipe.
4. Examine the tank itself: If the above steps don’t resolve the issue, inspect the tank for cracks, leaks, silt buildup, and proper pipework function.

Septic Tank Size: How Big Should it Be?

The size of your septic tank is crucial and depends on your water consumption. Factors influencing water usage include lifestyle, bathing preferences, and climate. Affluent households tend to waste more water.

American Calculation (Estimates)

• Formula: 0.95 cubic meters + 0.95 cubic meters per bedroom
• Examples:
  • 1 Bedroom: 1.9 cubic meters
  • 2 Bedrooms: 2.85 cubic meters
  • 3 Bedrooms: 3.8 cubic meters
  • 4 Bedrooms: 4.75 cubic meters
  • 5 Bedrooms: 5.7 cubic meters

British Calculation (from British Standard BS 6297)

• Formula: 2,000 liters (2 cubic meters) + 180 liters per person
• Examples:
  • 1 Person: 2.18 cubic meters
  • 2 People: 2.36 cubic meters
  • 3 People: 2.54 cubic meters
  • 4 People: 2.72 cubic meters
  • 5 People: 2.9 cubic meters
  • 6 People: 3.08 cubic meters
  • 7 People: 3.26 cubic meters
  • 8 People: 3.44 cubic meters
  • 9 People: 3.62 cubic meters
  • 10 People: 3.8 cubic meters

Modern Septic Tank Solutions

Plastic septic tanks are now available which are more resistant to ground movement than traditional brick or concrete block tanks.

By understanding how septic tanks work, identifying the causes of problems, and choosing the right size, you can ensure your septic system functions properly for years to come. Regular maintenance and prompt action to address issues can save you from costly repairs and health concerns.