I've been brainstorming over the last couple of days as to the motivation of a bathtub being ecstastic.
There are a few ideas now bouncing round my head.
1. A fat person is bathing and the bathtub is very uncomfortable it dances with ecstacy when its occupant finally leaves.
2. A beautiful bath is in a shop waiting to be bought and gets exited when someone comes in to buy it. Much like a dog gets exited when it finds a new owner.
3. Someone is singing in the shower and the bathtub unbeknown to the shower occupant is singing and dancing in accompaniment at the joyous rapture.
Edit: Moving further on idea 3. Say a man walks into the bathroom, turns on the radio to say 'Beat It' by Michael Jackson (just happens to be the baths favorite song), gets into the shower, back facing the bath. Bath hearing the song starts to tap his foot. Then breaks into some cool Wacko Jacko style dance moves ending with a moon walk. Somewhere in the middle the guys in the shower looks over his shoulder and the bath is instantly back in its normal position. This also happens at the end when the bath is moon walking.