[NYCAP123]

It's a very simple thing. Whether you're talking mud or c---. The solids fall to the bottom, the water rises. 6 months of no shaking and the pump out only takes the water on top. With home septic tanks you should put in a chemical like Rid-X that eats the ---- so the liquid can leach into the surrounding soil or else the tank volume shrinks and you bring in the big pumps. Eventually the bottom dries too much for the pump and it's time for a new septic tank, usually about 30 years or so. On boats we call it a brick and this boat has had 20 years to build it up. In a tank that was probably just 20 or 30 gals new that could do it.