The first step to understanding the consequences of not pumping is to understand how your septic system works. Your septic tank is designed to hold and process wastewater for only a day or two. This gives your waste the opportunity to separate. All of the solids fall to the bottom, liquids move to the middle and lighter liquids such as grease float to the top. Bacteria assists in the decomposition of the ultra light liquids, solid waste remains on the bottom of the tank for more long-term decomposition and everything in the middle gets pushed out as more wastewater comes in. In most cases, these liquids will wash into the drain field and dissipate without causing any trouble.