How often you need your septic system pumped depends upon the use it gets and the size of the tank. The following table is a good guideline, although specific systems and circumstances may vary. For example, a garbage disposal system increases the load by approximately 30%, meaning the system must be pumped more often.
Note that this presumes year-round occupancy -- obviously, seasonal use puts a lighter load on the system. Also note that this chart only applies to septic systems. It does not apply to simple holding tanks which retain all solid and liquid waste with no treatment or effluent disposal system.
| Table I. Septic Tank Pumping Frequency in Years | ||||||||||
| . | Household size - Number of Occupants | |||||||||
| . | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 |
| Tank-Gallons | Septic Tank Pumping Frequency in Years | |||||||||
| 500 | 5.8 | 2.6 | 1.5 | 1.0 | 0.7 | 0.4 | 0.3 | 0.2 | 0.1 | -- |
| 750 | 9.1 | 4.2 | 2.6 | 1.8 | 1.3 | 1.0 | 0.7 | 0.6 | 0.4 | 0.3 |
| 900 | 11.0 | 5.2 | 3.3 | 2.3 | 1.7 | 1.3 | 1.0 | 0.8 | 0.7 | 0.5 |
| 1000 | 12.4 | 5.9 | 3.7 | 2.6 | 2.0 | 1.5 | 1.2 | 1.0 | 0.8 | 0.7 |
| 1250 | 15.6 | 7.5 | 4.8 | 3.4 | 2.6 | 2.0 | 1.7 | 1.4 | 1.2 | 1.0 |
| 1500 | 18.9 | 9.1 | 5.9 | 4.2 | 3.3 | 2.6 | 2.1 | 1.8 | 1.5 | 1.3 |
| 1750 | 22.1 | 10.7 | 6.9 | 5.0 | 3.9 | 3.1 | 2.6 | 2.2 | 1.9 | 1.6 |
| 2000 | 25.4 | 12.4 | 8.0 | 5.9 | 4.5 | 3.7 | 3.1 | 2.6 | 2.2 | 2.0 |
| 2250 | 28.6 | 14.0 | 9.1 | 6.7 | 5.2 | 4.2 | 3.5 | 3.0 | 2.6 | 2.3 |
| 2500 | 30.9 | 15.6 | 10.2 | 7.5 | 5.9 | 4.8 | 4.0 | 3.5 | 3.0 | 2.6 |
A more precise way to tell if it's time to pump the tank is to measure the thickness of the scum + the thickness of the sludge. The total should not exceed 1/3 of the tank depth:
Remove the inlet chamber access riser cover. Using a long stick, marked off in inches or centimeters, slowly push through the hard layer of floating scum on top. You will be able to tell when you have pushed through by the sudden lack of resistance. Note the measured thickness. Now continue to slowly lower the stick until you meet some resistance again. That will be the top of the sludge layer. Note the measurement. Continue to push down until you hit the bottom of the tank and note the final measurement.
For example: The stick pushes through 8 inches when resistance stops. That means the scum layer is 8 inches thick. Resistance is noted again at 3 foot 8 inches and the bottom of the tank is hit at 4 foot six inches. That means the sludge layer is 10 inches thick.
8 + 10 = 18 inches (or 1-1/2 feet). One third of 4-1/2 feet is 1-1/2 feet, so it's time to pump the septic system!
Note: even though the second chamber will have less sludge and scum, both chambers need to be pumped at the same time. If you have a filter on the outlet, it should be cleaned now too.