Er....really?!
I've seen this film this film a couple of times, it's alright...but I've just been on Wikipedia and the plot summary says THIS about the scene near the end when Drew and Skerritt are doing it by the piano:
"Upon returning home, Sylvie finds Ivy and Darryl stimulating each other anally on the piano."
Really!? I didn't notice that, I thought it was just a bit of bog standard sex.