Step 4 · Inspect Septic Tank Interior

With the lids removed, use a flashlight to inspect the interior of the septic tank. Observe the layers of scum (solids floating on top) and sludge (solids settled at the bottom). The tank generally needs pumping when the scum layer is within 6 inches of the bottom of the outlet baffle or the sludge layer is within 12 inches of the top of the tank. You can use a measuring stick or a long pole to gauge these levels. Also, look for any signs of inflow or outflow pipe blockages.