Our mall has a hottub-o-thon, however, its probably different then how a fraternity or sorority does it.
It was a contest where people were drawn, and if they won, they were allowed to sit in a hot tub. The people had to stay in the hot tob at all times, and the person who stayed in it the longest (I think it was like 48 hours) got to take it home. The tubs werent full (of water) though.
I imagine if a greek house did it, there would be more social interaction.