The Teapot That Reverses Time, a time travel teapot, is one of Tim Jones' many inventions. When he originally conceived it, he felt it "isn't going to cut it" when it came to trying to "improve humanity's lot", so he brainstormed for more useful ideas, arriving at the idea of breeding "the meanest, angriest wasp ever." At that point, his alternate-future self, with an eyepatch and a teapot, appeared to dissuade him of pursuing this idea, and give him an alternative idea of building a robot girlfriend for Rich Tweedy, which turned into Unit Daisy.
Years later, when Amy Chilton is working as Tim's assistant, she sees the teapot and expresses interest in using it to relieve her boredom, but Tim doesn't want her to do this because of possible harm to the space-time continuum caused by irresponsible time travel. Amy then returns to Tim's house at night with Shelley Winters (who is drunk) to steal the time teapot, planning on having an adventure with it and then returning to the same time they started so that Tim will never notice.
The two women travel back to the 1800s, with Shelley introducing the music of the Beatles (or is it The Beetles?) to an earlier era (claiming credit for the songs herself), and Bob Crowley making an appearance in his original 19th-century lifetime (his 21st-century afterlife self would later be important to some earth-shaking plots). However, (meanwhile back in the future) Tim has received notice from his Trouble-O-Tron, which detects problematic situations, that the time machine has been taken, and uses another time teapot (he turns out to have a whole cupboard full of them) to go back in time to the minute before the time teapot is stolen and stop Amy and Shelley outside his house before they break in. Thus, the whole time travel adventure never happened, a fate common to time excursions in the Tackleford universe. Amy is fired as Tim's assistant due to this, perhaps a little unfairly because Tim manages to do the firing prior to her actually stealing the time teapot. thus punishing her for something she didn't do.
A perfectly scientific explanation for it Edit
As The Boy (another of Tim's assistants) explains it, the time teapot works by having a heating element in the bottom and an electric eye in the lid. The water heats up but can never boil (you know about "watched pots" and all that), causing time to get confused and align itself to the nearest clock, which is mounted in the side of the pot. Thus you can set the clock to the desired destination time. Just how you adjust an analog clock to a date in a past century is unexplained.