Verify the inputs
Measure or document each input. If a value is only an estimate, record its source and test a conservative alternative.
Wastewater/ CALCULATOR
Septic solids service interval
Use measured sludge and scum layers to estimate when a chosen service threshold may be reached.
FROM ESTIMATE TO ACTION
Use the result, not just the number.
Keep the calculation traceable
Save the input link or copied result together with the date, units and assumptions. A number without its inputs cannot be checked later.
Confirm the decision
Compare the estimate with the related guide, current product data and requirements that apply at your location before buying or building.
Inputs to verify
- Normal liquid depth (cm)
- Measure or obtain the depth from the tank bottom to the normal liquid level.
- Measured bottom sludge depth (cm)
- Use a safe measurement made from outside the tank by a qualified person.
- Measured floating scum thickness (cm)
- Use layer thickness, not the distance from the cover to the top of the layer.
- Chosen combined-layer service threshold (% of liquid depth)
- Enter the threshold required by local guidance or the service provider; 33% is only an example.
- Observed combined-layer growth (cm/year)
- Prefer the change between two comparable measurements. Do not invent a rate from tank age alone.
- Planning margin before threshold (months)
- Allow time for seasonal access, booking and uncertainty.