i just finished replacing the flappers and seat discs in all 6 of our toilets. i've color tested them for leaks and a few of them have a slight leakage (maybe a few drops, less than an ounce) over a several hour period. a flapper is never actually 100% water tight is it? BTW most are old kohlers and one american standard vent away. and, yes, i know i should replace them all, but color matches and cost are obstacles right now.