You may imagine your septic tank takes a long time to fill up after you've had it pumped out, and once it's full, it's time to pump it out again. If so, you may be surprised to know it only takes a few days for the tank to become full again. The key is what's inside the tank. If it's mostly water, your tank is okay. It there is only a small amount of water squeezed between a thick layer of sludge on the bottom and a layer of oil on the top, your septic tank needs to be pumped soon. Here's more information on how this works.
The Drain Is In The Middle
A septic tank is designed with the outlet to the drainfield in the middle area of the tank. That keeps the sludge on the bottom