B737-800 Flight Attendant reported waste water and sewage were leaking from a lavatory during a flight sequence. After reporting it to the Captain; the discrepancy went unaddressed by the flight crew and maintenance.

Narrative

This report is being submitted as a health and safety concern for passengers and crew on the aircraft. Upon landing in ZZZ; the D Flight Attendant (FA) and I noticed a distinct sewage odor and the literal flood of water coming from one of the AFT Lavs (First Officer side). I called the Captain to report and we agreed to monitor it for the turn to ZZZ1. The stench and water collection in the galley and outside the lav continued on both legs. I again called the Captain to report and they said and I quote; 'tell the maintenance staff coming to fix some bin molding; and they can look at it.' It was the end of their trip and they were commuting home after the leg. Maintenance came onboard and confirmed we had an issue and indeed did smell sewage. They told us that the galley 'mat' had obvious bubbling consistent with this kind of leak. They said the fix would involve taking this newer aircraft out of service; removing the mat; letting it dry completely; treating the area with a product to eliminate the germs and bacteria; and replacing the mats in the galley and lav. There was obvious buckling and bubbles in both areas and the area outside the lav had a visible brown/gray area.It was again decided by our new Captain to have it looked at in ZZZ2; which was a Maintenance base and our final destination. Once in ZZZ2; Maintenance came on; and told me this aircraft had a long history with the leaking lav and the sewage smell. I asked them why we wouldn't fix it and they said it would be a long fix; it wasn't the end of day for the aircraft; and they only took care of these issues when they were terminating flights. A passenger; was seated in 30D and they said it was definitely a strong sewage smell; which they said they smelled throughout the flight. I am honestly appalled we continue to allow aircraft with these types of issues to remain active without a maintenance fix for a blatant and serious health risk to crew and passengers. Having to smell that sewage for our entire duty day was horrible. Sewage and gas odors such as this present health risks and are toxic to the system. I coughed all day yesterday; had a runny nose; eye tearing and felt periodic nausea. It was truly disgusting.