Help needed - which episode???

My favourite line of dialogue is when Chorlton meets a duck who keeps diving below the water to feed. Chorlton says something like " Eeee, your bum looks like your face."

The duck replies, in a Mexican accent if I remember correctly, "It's better to have a bottom like a face than to have a bottom like half a ton of salami!"

Anybody know the correct dialogue and which episode?