Most septic tanks need to be pumped every 3 to 5 years depending on how big the septic tank is and how often you send solids down the toilet.
You can use RidX to help keep the solids broken down in the septic tank which keeps it from filling up too fast.
Some signs that your septic tank needs pumped out are backing up sewage, over healthy lawn, green lawn near the septic tank.
Other signs that your septic tank needs pumped and is full is slow drains, or a toilet that is slow to flush.