"A good waste extraction system is important. Imagine where we'd be without one." - Rom
The waste extraction system, also known as the waste reclamation system, sewage and waste reclamation, or the sewer, was a plumbing system used to manage and process all bodily wastes aboard starships and starbases.
In 2369, Doctor Julian Bashir took cell samples from the entry of the waste extraction system aboard a Bajoran transport to identify the DNA of the murdered Bajoran criminal Ibudan and possible other DNA. (DS9: "A Man Alone")
The same year, the Kobliad criminal Rao Vantika placed a subspace shunt in the waste reclamation system to sabotage Deep Space 9 and hijack the deuridium shipment from the Gamma Quadrant but Lieutenant George Primmin found this device. (DS9: "The Passenger")
On stardate 48892.1, The Doctor, while in a malfunctioning holodeck program (which he believed to be real life), requested a ship-wide system update and the computer reported sewage and waste reclamation as one of them. At the time, it was presumably offline as with almost all other systems. (VOY: "Projections")
In 2373, Rom quit his job at Quark's to pursue a position working as a technician for the Bajorans. His first assignment was working the night shift on Deep Space 9's waste extraction system. (DS9: "The Assignment")
Working in waste extraction was typically considered the least desirable posting for an engineer. (DS9: "The Assignment") After Enrique Muñiz called Miles O'Brien a "mountain man... an old mountain man", O'Brien asked him how he would like a transfer to Deep Space 9's waste extraction unit. (DS9: "The Ship") Another engineer, Pechetti, was previously assigned to waste extraction before volunteering to join the salvage team that "raided" Empok Nor. (DS9: "Empok Nor")