one common misconception is when people ask if their septic tank is full. Technically, a septic tank is always "full" as you can see in the diagram on this page. The liquid level rises until it reaches the outlet pipe in your septic tank, where it then flows into the leach field.
Determining when to pump your septic tank depends on a few factors. Normally we recommend for 1000 gallon tanks to be pumped every 3 years and a 1500 gallon tank to be pumped every 5 years. However, if you have many people in your home you may need to pump your tank more often.
We get this question a lot. Some people will say "Ive never had my septic pumped in 20 years and its still working fine!" Although your toilets may still flush, we don't recommend this. Over time, the "sludge" layer in your septic tank will keep building until eventually there is very little liquid left in the tank. When this happens, the "sludge" layer begins to travel into your leach field which will eventually cause total failure. Its much more cost effective to regularly maintain your septic than to risk having to need costly repairs