• Sewage Backup in Drains. The most noticeable and most severe sign of an overfilled septic tank is sewage backing up into your home’s drains. …
• Changes in Your Lawn. In some cases, a backed up septic tank may cause changes outside your home before changes begin inside. …
• Foul Odor Inside or Outside. …
• Too Long Since Last Pump.

When your septic tank is excessively full, your toilet may start acting odd. You might find that your toilet doesn’t fully flush or flushes very slowly and odd noises occur when you flush your toilet

Septic tanks gradually fill with solid waste. The grey water is allowed to pass through the tank and out into the underground drain field lines in your yard. Once the tank is full of solid waste, you may experience sewage backups in the toilets or slow drains in tubs and sinks.