Tool
Pump-due calculator
Idaho DEQ and SIPH tell homeowners to pump every 3–5 years and to measure sludge and scum sooner if the house is hard on the tank. This calculator turns tank size and occupancy into a planning interval. It does not replace a measuring stick in the lid.
What the math is doing
The estimate uses a simple solids-accumulation model: treat about half the tank as the working clear space, and assume on the order of 50 gallons of sludge and scum per person per year. A garbage disposal shortens the interval. Heavy use shortens it again. The result is then compared with Idaho’s 3–5 year pumping range and with EPA/SIPH measurement triggers.
If the model says 12 years because one person lives with a 1,000-gallon tank, do not wait 12 years. Check levels at least every three years anyway. If six people share that tank, do not wait for the calendar; measure this year.
Pump now if measurements say so
SIPH and EPA agree on the field test, independent of this calculator:
- Bottom of the scum layer is within 6 inches of the bottom of the outlet
- Top of the sludge layer is within 12 inches of the outlet
- Sludge and scum together are more than 25% of the liquid depth
DEQ’s pumpers’ manual adds the 40% sludge-volume and “scum at the top of the baffle” limits. Any of those beats a calendar.
Write the numbers in the maintenance log so the next pump-out is based on your tank, not a statewide slogan.