Longest time before emptying black tank?

I have left black tank over several months.. and as long as I ensured plenty of water, no issues.. Used TT just before Thanksgiving and ran into issues that I didn't dump. Fast forward to early March before I got trailer out.. used it that weekend and then dumped. Just ensured I put lots of water in it. Also I kept a jug of water in the bathroom, and periodically poured water into bowl. it seems the seal is either not completely watertight or water in bowl would evaporate.. keeping water in bowl over seal seems to be key to keeping smell out.