Good in theory, but they just don't work. A hard nylon or copper drain plug gasket, combined with a smooth, flat surface to seal against is the best of all possible situations. I like to draw-file the pan area around the plug to make sure there's not a pulled thread or other irregularity that prevents the washer from getting a good seal.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!