How often does your septic tank need pumping?
Pick your tank size and how many people live in the house, and the tool reads the years between pumpings from Oregon State University Extension's EC 1343, Table 1. That is an Oregon table, not a Michigan rule: EPA says pump every three to five years and EGLE says pump when the tank is more than one-third full, and the tool shows both beside the answer.
Answer the questions
The table behind the calculator
| Tank size | 1 person | 2 people | 3 people | 4 people | 5 people | 6 people | 7 people | 8 people | 9 people | 10 people |
|---|---|---|---|---|---|---|---|---|---|---|
| 500 gal | 5.8 | 2.6 | 1.5 | 1 | 0.7 | 0.4 | 0.3 | 0.2 | 0.1 | no value |
| 750 gal | 9.1 | 4.2 | 2.6 | 1.8 | 1.3 | 1 | 0.7 | 0.6 | 0.4 | 0.3 |
| 1,000 gal | 12.4 | 5.9 | 3.7 | 2.6 | 2 | 1.5 | 1.2 | 1 | 0.8 | 0.7 |
| 1,250 gal | 15.6 | 7.5 | 4.8 | 3.4 | 2.6 | 2 | 1.7 | 1.4 | 1.2 | 1 |
| 1,500 gal | 18.9 | 9.1 | 5.9 | 4.2 | 3.3 | 2.6 | 2.1 | 1.8 | 1.5 | 1.3 |
| 1,750 gal | 22.1 | 10.7 | 6.9 | 5 | 3.9 | 3.1 | 2.6 | 2.2 | 1.9 | 1.6 |
| 2,000 gal | 25.4 | 12.4 | 8 | 5.9 | 4.5 | 3.7 | 3.1 | 2.6 | 2.2 | 2 |
| 2,250 gal | 28.6 | 14 | 9.1 | 6.7 | 5.2 | 4.2 | 3.5 | 3 | 2.6 | 2.3 |
Estimated septic tank pumping frequencies in years (for year-round residences). Source: Oregon State University Extension Service, EC 1343 "Septic tank maintenance", Table 1 (revised March 2022, reviewed 2025). Calculated for a minimum of 24 hours of wastewater retention and 50 percent digestion of retained solids. The 2,500-gallon row is not used because its values for five and six people do not follow the pattern of the other rows.
What the agencies say
- EPAInspect every one to three years and pump every three to five years; pump sooner when scum is within 6 inches of the outlet bottom, sludge within 12 inches of the outlet, or sludge and scum exceed 25 percent of the liquid depth.
- EGLEPump if the tank is more than one-third full of scum and sludge. EGLE does not recommend additives.
- Monroe CountyRecommends pumping by a licensed pumper every one to two years (advice, not a rule).
- Barry-Eaton District Health DepartmentTells Eaton County homeowners that pumping every two to three years is typical (advice, not a mandate).
Every possible result
The result above appears when scripts are on. Each result below is listed with the answers that lead to it, in the order the tool checks them.
- You use a garbage disposal. Oregon State's table notes that tanks need more frequent pumping with one, and EGLE says a disposal increases the sludge and scum and how often the tank may need pumping. Neither gives a factor, so treat the table figure as a ceiling and have the sludge measured.
- If a disposal is wired in under the kitchen sink, count it. Both Oregon State and EGLE say it means more frequent pumping.
- The table makes no adjustment for a softener or reverse osmosis unit. EGLE says residential septic systems in Michigan are not designed for softener backwash, that most local sanitary codes prohibit connecting such discharges, and that a reverse osmosis unit can discharge four gallons per gallon filtered. The answer is to reroute the discharge, not to pump more often. Ask your county health department what your code says.
- Ask your septic company or installer where the softener backwash goes. EGLE says residential septic systems in Michigan are not designed for it.
Under a year: the tank looks small for the household
Chosen when: Table reading: years < 1.0
Oregon State's table gives less than a year between pumpings for this combination, which usually means the tank is small for the number of people. Do not wait for a year to pass. Ask a licensed pumper to measure the sludge and scum, and ask the county whether a larger tank is possible. The Michigan Criteria set 1,000 gallons as the minimum for a new system.
Septic pumping · How often to pump a septic tank in Michigan: the table, the agencies and your county
One to three years: more often than EPA suggests
Chosen when: Table reading: 1.0 <= years < 3.0
Oregon State's table gives one to three years, shorter than the three to five years EPA recommends for an average household. Use the table as the planning figure and have the sludge measured at each pumping. EPA's tests are scum within 6 inches of the bottom of the outlet, sludge within 12 inches of the outlet, or sludge and scum above 25 percent of the liquid depth.
Septic pumping · How often to pump a septic tank in Michigan: the table, the agencies and your county
Three to five years: inside EPA's range
Chosen when: Table reading: 3.0 <= years <= 5.0
Oregon State's table lands inside the three to five years that EPA recommends. EPA also recommends an inspection every one to three years, and EGLE's test is to pump when the tank is more than one-third full, so book an inspection between pumpings.
Septic inspection · How often to pump a septic tank in Michigan: the table, the agencies and your county
More than five years in the table: inspect anyway
Chosen when: Table reading: years > 5.0
The table gives more than five years, which is the top of EPA's range and of Oregon State's own summary. That summary says a properly designed system's tank should be inspected and pumped every one to five years. Treat a long table figure as a ceiling, not a schedule: EPA still recommends an inspection every one to three years, and a measurement tells you more than a table.
Septic inspection · How often to pump a septic tank in Michigan: the table, the agencies and your county
The table gives no value for this combination
Chosen when: Table reading: cell is empty
Oregon State's table has no value for a 500-gallon tank with ten people, and a tank that small for that many people needs a professional's measurement, not a table. Ask a licensed pumper and your county health department.
Septic pumping · How often to pump a septic tank in Michigan: the table, the agencies and your county
Find the tank size first
Chosen when: Table reading: You answer that you do not know the tank size
Without the tank size the table cannot help. Your county health department usually holds the permit and the as-built drawing, according to EPA, and a pumper can read the size when the tank is opened. Older Michigan houses can have tanks smaller than the 1,000-gallon minimum the Criteria set today, and smaller tanks fill faster.
Septic inspection · What a septic pumping receipt should show in Michigan
This is an Oregon table, calculated for year-round residences, and it is not a Michigan rule: we found no Michigan law that sets a pumping interval. It is a planning figure. A pumper's measurement of your own sludge and scum is the better answer, and Michigan counties may advise something different.
We are a referral service, not a septic service company. How we check what we publish.
- Oregon State University Extension Service, EC 1343 "Septic tank maintenance" (John Talbott; revised March 2022, reviewed 2025), Table 1 Read Oct 19, 2026.
- Michigan Criteria for Subsurface Sewage Disposal, section VIII Read Oct 19, 2026.
- EPA: Why Maintain Your Septic System Read Oct 19, 2026.
- EPA: How to Care for Your Septic System Read Oct 19, 2026.
- EGLE FAQ: Septic systems; EGLE SRLP Program Minimum Standards Read Oct 19, 2026.
- EPA: Frequent Questions about Septic Systems Read Oct 19, 2026.
- Septic System Read Oct 19, 2026.
- On-Site Sewage Systems Read Oct 19, 2026.
Request sent
We passed your job request to one septic service company that works your area.
- 1The company, or a referral partner acting for it, calls the number you gave.
- 2You agree the job and the price with the company, in writing.
- 3If you do not hear from a company, tell us through the contact page.
- Find the tank lid, or ask the county for the as-built drawing.
- Clear a path for the truck to within hose reach.
- Note the tank size and the date of the last pumping if you know them.
- Ask for the sludge depth and the condition of the baffles on the receipt.