About 5 years ago I installed a Toto/Drake toilet in our main bathroom. It has worked flawlessly although the flush has always been a little noisey. Recently the Gmax valve seems to have developed a problem. After flushing it may be 20 seconds or so before the valve lets water start flowing into the tank. Has anyone encountered this problem or know the cause of it? This "problem" is something we can live with but my concern is that eventually the delay may get longer until it no longer allows water into the tank.