You searched for: “septic tank
septic tank (s) (noun), septic tanks (pl)
A large storage container where solid matter or sewage is disintegrated by bacteria: Dick bought a septic tank for his farm because he was too far away to take advantage of a community sewage system.

If you would like to learn about septic tanks for a better understanding of this important subject, you may do so from here.

(There are septic tanks and then there are septic tanks)