I have a Toto G-Max 1.6 gpf toilet which I installed in 2003. It has a 3" dia tank drain. At the time I believe it was mandatory to convert to the low gpf system if one needs to replace the standard 6 gpf toilet. But since I've had this type toilet,occasionally I've had to flush the toilet a second time to get rid of the waste. I did a little investigating and found out that the flapper valve which has a side vent hole shuts down too quickly, disallowing enough water to go down and does not allow enough water to go down the fill tube. I checked a couple of hardware stores and discovered that many of the models have now 4" tank drains and that the fill valve has increased capacity to direct more water to to the bowl via the fill tube. Also there is now a device whereby the size of the side vent in the flapper valve can be adjusted. So to solve my flushing problem, I replaced the fill valve with a high capacity model, cover up the side vent on the flapper valve and now I never have to do a second flush. The water level is still as designed (1" below the rim of the fill tube. My question is: Has anyone ever experienced the phenomenon I stated above? Did the industry have to do some alternation to the original design? I'd like to listen to your comments.