a tank in which solid organic sewage is decomposed and purified by anaerobic bacteria.
Origin of septic tank
First recorded in 1900–05
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019
a tank, usually below ground, for containing sewage to be decomposed by anaerobic bacteria
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012