I got that lock with my second character. The first one jammed it...
That lock is a case where Mama Hissy's words ring true... Save early, save often, SAVE BEFORE, save after. Save before attempting the lock, and when you fail, reload. I only had to do it about three or four times... and I used the level three lockpick as well.
You basically have to do it the same way as the chests -- click on the correct tumblers when it they're active.
BTW, I have discovered something rather annoying -- when you've got level 4 lockpicking skill, your odds on a level 1 lock are 99%... and the little red activation bar CRAWLS across the screen! I mean, if the tumbler is the last one, you could click disarm, get up, go to the bathroom, come back, and it will almost be there. It's almost as bad as Sebastio talking!
I also have a combat tip that I've found useful against slimes. If they gas you, it takes a few seconds to cough and gag it out of your system. If you're next to them, however, they will keep attacking and may gas you again. What I do is to double-tap the forward key (to launch into a roll) several times, changing directions if needed. They will chase you and won't gas you until you're close again. The roll gives you more time to get away and recover... typically, it takes about three rolls from what I've seen.
Which key do you have to swim to, mighty stamar? I've got the theater key and skull key, and I'm wondering if I missed something.
Oh, BTW... I mapped out most of the sewers last night so I could stop getting lost. When I get a chance, I'll transcribe it electronically and post it somewhere. Much easier after mapping...