the same thing happened to lonnie! (see: http://www.bettafish.com/showthread.php?t=53275
) except he went all the way down to the bendy part! needless to say, I FREAKED OUT! I was SCREAMING at the top of my lungs until my dad ran upstairs, saw what happened, ran back down stairs, and ran back up stairs with a large wrench, took what seemed like hours to unscrew the pipes, and finally rescued my beloved fishie! but he is alive and well today!
I'm glad Sam didn't go all the way down the drain, and that he's OK. bettas are tough little critters, and I'm sure he'll be fine! oh, and be sure not to use the AQ salt for more than a week at a time. (then, after another two weeks, you can repeat the treatment)