Well, the leak hasn't reoccured. Monday night I checked it out and it appears that it was just stink-water that had condensed inside my exhaust. My theory is that there is a small hole in the exhaust, and the water would only leak out when the pressure increased in the pipe(from, say, a running engine) .
It's been rather humid here. Sunday night was unusually cool and the problem hasn't come back all week. So either my theory was correct, or the ride bell Lady Luck gave me really works. I'll write more about the ride bell later.