What is a septic tank? It is a container that is buried underground. It is water-tight and made of concrete, fiberglass, or polyethylene.
The job of a septic tank is to hold the wastewater that exits your home and separate the waste from the water by making use of natural processes and proven technology.
Septic tank history
Way back when tanks were homemade, they came in a variety of sizes and materials. In the 40s & 50s, they started building the concrete box, a single compartment, but it did standardize the tank a bit. In the late 70s, they came to adopt the standard size of 1000 gallons and put in a wall and divided the tank for better settling.