Normally, properly designed tanks have enough space for up to three to five years' safe accumulation of sludge. Beyond that point the sewage will have less time to settle properly before leaving the tank. That causes the solids to escape the tank and will over time clog the drain field or pump on your aerobic system causing it to burn up. So since the field lines are clogged it could lead to your plumbing backing up or unsanitary waste bubbling to the surface. With that being said, just because you're not having an issue doesn't mean you don't need your system pumped out. This is a common misconception by an amazing amount of system owners that could lead to costly repairs. So don't wait til its too late.
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