Your septic tank is a fairly simple device. When you flush your toilet, water goes down the drain, or if you run your shower, water goes through pipes into your septic tank. The septic tank separates your waste into three different levels. The top layer is oil and fat that rises to the top because it is not water soluble. The bottom layer is solid waste that automatically sinks to the bottom. The middle layer is wastewater. The wastewater is actually drained out of the septic tank into the drainfield. If you need septic tank repair, it is likely a problem with your drainpipe or drainfield.