If the episode aired at 6(pm?), it's reasonable to assume you saw a syndicated episode. Different episodes air in syndication around the country (& world) and since no one has any idea where you are or what channel you saw it, not to mention you provided no information about the episode & the episode aired 14 years ago (as of this answer) this question is impossible to answer.
October 2, 2000 for "Under the Night".
The Simpsons - 1989 26-2 was released on: USA: October 2014
The Simpsons - 1989 Eight Misbehavin' 11-7 was released on: USA: 21 November 1999 UK: 2 January 2000 Germany: 9 October 2000 Hungary: 15 December 2001
Season 19 episode 2. It's called The Homer Of Seville
The Simpsons - 1989 Cape Feare 5-2 was released on: USA: 7 October 1993 UK: 10 October 1993 Hungary: 18 January 1999 Germany: 2 October 1999
The Simpsons - 1989 Bart Stops to Smell the Roosevelts 23-2 was released on: USA: 2 October 2011 Hungary: 28 October 2012
Yes, Christoph Waltz guest stars in an episode of "The Simpsons." He appears in Season 34, Episode 2, titled "The Burn and the Bees." In this episode, he plays a character who interacts with the show's main cast, showcasing his distinctive voice and acting style.
The episode was promoted with 2 items, Oscar's Obstacles Truck & the USS Tom Clancy
The Simpsons - 1989 It's a Mad Mad Mad Mad Marge 11-21 was released on: USA: 14 May 2000 UK: 8 October 2000 Germany: 5 February 2001 Hungary: 2 February 2002
"New Kids on the Blecch"1214 CABF12Original Airdate: 2/25/01
O Fortuna.
Nothing happens in the 3000th episode because The Simpsons will never reach 3000 episodes.The Simpsons only air 22 episodes a season so at that rate it would take 136 years (from its initial debut) to reach 3000 episodes & it's absolutely impossible the show will still be on the air in 2126.