Foul odor: This will resemble a rotten egg or sulfuric smell emanating from your pipes, with the smell getting worse outside where your septic tank is located.
Slow drainage: Slow drainage in your kitchen or bathroom could point to a plumbing issue, but might also diagnose a potential septic tank problem.
Pooling water: If your septic tank has reached capacity, the solid waste can clog the drain field, causing pools of water to form above ground.
Sewage backup: A sure-fire sign your septic tank has reached capacity.
Gurgling pipes: Hearing gurgling noises after you flush your toilet or run the water can be an indicator that your septic tank is full and in need of pumping.
Disproportionately lush lawn: While this might not seem like a problem, if grass around your septic tank is growing greener or faster than the surrounding areas, it can be a sign that your tank is leaching fluid.