B737-700 flight crew reported lavatory leaking into cabin and cockpit area.

Narrative

Received aircraft XXX in ZZZ; with a history of forward lavatory issues documented and subsequently cleared in the logbook. Approximately halfway between ZZZ and ZZZ1; we were advised; by the Flight Attendant; that the forward lav was leaking sewage onto the floor. Sewage then began seeping into the flight deck from under the second jump seat. The First Officers bag was damaged with the sewage spill. Brown sewage was also leaking into the flight deck area behind the center pedestal. We continued into ZZZ1 for an uneventful landing. Maintenance was notified and a logbook entry was made. ZZZ1 Maintenance removed the toilet seat cover to find a leaking line that they were unable to repair. The forward lavatory was locked and deferred per MEL XX-X-XX Lavatory Not Used. About halfway into our next flight; ZZZ1 to ZZZ2; the sewage reappeared in the same areas. The Flight Attendant then called to say the lav smelled horrible and that the aircraft was unsafe to continue on. I agreed and sent a Maintenance Message informing ZZZ2 Maintenance of the issue. We landed safely in ZZZ2 and assumed the aircraft would be grounded. I contacted Maintenance through Dispatch; to tell them the Supervisor on Duty should put in a swap. I met local Maintenance and advised them of a puddle of sewage on the flight deck. I told them it was unsafe for use and they agreed saying; 'We'll take it to the hangar.' Walking to my car; I was contacted on my personal phone by Scheduling; saying I had to call Maintenance Control. I then called Maintenance Control and was told with an attitude that 'I just can't ground an aircraft and walk away; and where's the write-up?' I then replied 'hold on a second;' to which the Controller responded; 'NO YOU HOLD ON A SECOND!'I then told him that I would walk back across the street to write it up. However; it was now on a deferral and had flown around for two days without being repaired; while creating an unsafe environment for passengers and crew. He then said; 'What do you want in the logbook?'; to which I replied 'aircraft unsafe for use due to forward lavatory leaking sewage into flight deck area and Flight Attendants report forward lavatory excessive sewage smell' He then hung up. I simply didn't see the need for additional logbook write-ups when Maintenance was literally standing in a pool of sewage in the flight deck. Apparently the previous deferral didn't work. However; the Maintenance Controller was apparently unhappy with me for not re-entering the deferral??? I have never received a personal phone call; while off duty; or been treated so disrespectful; by another employee in my over XX years at this Company. The pressure and coercion to keep aircraft in service is a severe Safety issue to our passengers and crew. The Maintenance Controller should be removed from duty and retrained. Personally contacting a Captain to tell him he can't ground an aircraft without a logbook entry; is promoting a hostile; unsafe work environment. I exercised my Captains authority to provide a safe; hospitable environment for my passengers and crew; by grounding the aircraft. My First Officer and I both returned home from our trips with sewage-laden bags. My bag was subsequently left in the sewage when my First Officer pulled his bag out. The Flight Attendant was required to serve drinks out of a galley adjacent to this lavatory for two flights; thanks to our Maintenance Operation's incompetence. I wrote it up and was in compliance with our MEL procedures. I then followed up to Dispatch and Maintenance Control; only to be met with attitude and told you can't do that. The Company should issue vouchers to the passengers affected on this flight from ZZZ1 to ZZZ2. The Company should offer to replace the First Officer's and Captain's luggage and issue a stipend for belongings damaged.