Home › Words › S › septageseptage/ˈsɛptɪd͡ʒ/septage means the partially treated waste stored in a septic tank.septage is pronounced /ˈsɛptɪd͡ʒ/.EtymologyFrom sept- as in septic + -age.nounThe partially treated waste stored in a septic tank.Definitions & examples from Wiktionary (CC BY-SA 3.0).