Basil the Rat (a.k.a. Rats) - S2-E6
Trivia: Melody Lang, who plays Mrs. Taylor in this episode, is Andrew Sachs' wife.
Trivia: Sybil's friend, Audrey, who Sybil is frequently seen talking to on the telephone, has only one on-screen appearence in 'The Anniversary'. She is seen at the very end, when Sybil has just walked out on Basil.
Trivia: For one episode, the props guy spent ages building up the bottom of a frying pan with cotton wool and padding, then painting it black to look right. It was placed on a shelf just inside the kitchen door. Unfortunately, on the night, John Cleese reached around the door frame without looking and picked up the wrong frying pan. He then hit Andrew Sachs very hard over the head with it, almost knocking the poor man out.
Trivia: The program is based on a hotel in which John Cleese and Connie Booth stayed in Torquay. Noted in the Series 1 dvd notes.
Trivia: John Cleese has said that the character of Major Gowen was based on his Latin teacher from school.
The Germans - S1-E6
Trivia: Although this episode is entitled "The Germans", the first German guest we see doesn't appear until 23 minutes into the episode.
Trivia: There is only one episode in which the anagram on the sign uses all the letters, reading "flowery twats."
The Germans - S1-E6
Trivia: This is the only Fawlty Towers episode that doesn't have a hotel sign at the beginning. The episode opens at a hospital.
The Germans - S1-E6
Trivia: The hospital used during the opening titles is Northwick Park Hospital in Middlesex.
Communication Problems (a.k.a. Theft) - S2-E1
Trivia: On the episode "Communication Problems", when Mrs Richards is in the staff office claiming that her money had been stolen, Basil wound her up by suddenly shouting at her. When she banged her head on the shelf, Basil bent down and said, "Is this a piece of your brain?" which is an iconic moment of that episode. However, John Cleese wasn't originally going to put that line in, and had it cut out because he "didn't like it". Andrew Sachs, however, told him to put it back in because he wouldn't regret it, and so he did. Sachs himself claimed on Fawlty Towers: Basil's Best Bits that it was his "one contribution to rescuing the script."
Basil the Rat (a.k.a. Rats) - S2-E6
Trivia: In some shots of this episode, a real rat was used. These shots were pre-recorded due to the production team having concerns that it could run into the studio audience.
The Builders - S1-E2
Trivia: You will probably recognise the actor who plays Lurphy in this episode - it's Michael Cronin, best remembered as the PE teacher Geoff "Bullet" Baxter in the children's show "Grange Hill".
The Germans - S1-E6
Trivia: In this episode, the jacket Andrew Sachs wears was treated with acid by the special effects department to look as if it was really on fire. Unfortunately it really did burn through to his skin and he bore the scars until he died in 2016. Sachs was paid damages by the BBC.
Answer: It's "Leisure Complex" by Dave Gold and Gordon Rees. Can be found on YouTube. The relevant clip is around 25 seconds in.