The Wedding Party (a.k.a. Sex) - S1-E3
Basil: Did you ever see that film, "How To Murder Your Wife"?
Major Gowen: How To Murder Your Wife"?
Basil: Yes, awfully good. I saw it six times.
Gourmet Night (a.k.a. Gourmet's Paradise) - S1-E5
Sybil Fawlty: Are you going to do the car?
Basil Fawlty: In a minute, my little piranha fish.
Basil: Hello? - Ah, yes, Mr O'Reilly, well it's perfectly simple. When I asked you to build me a wall I was rather hoping that instead of just dumping the bricks in a pile you might have found time to cement them together...you know, one on top of another, in the traditional fashion.
The Germans - S1-E6
Basil: Don't mention the war. I mentioned it once, but I think I got away with it all right.
The Wedding Party (a.k.a. Sex) - S1-E3
Basil: Hello, Fawlty Titties.
Answer: It's "Leisure Complex" by Dave Gold and Gordon Rees. Can be found on YouTube. The relevant clip is around 25 seconds in.