I also have a 9.1 Aft cabin S2 and my holding tank is under the port side berth in the main cabin.
Mine leaked and I replaced it (tanks come in a myriad of sizes/shapes). The main thing I found out (the hard way) is that you must use "impermeable to gas" hoses. Don't simply buy hoses at Walmart and expect no odors. Odors penetrate most hose walls so you need to buy gas impermeable hoses....or expect odors continuously.
If you need help in finding a tank, send me a not (pappaboat@gmail.com) and I'll get you a contact.
Skippie