How is the toilet made the difference between 1.28 and 1.60 GPF toilet?

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compiler

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Does the 1.28 GPF just flush less water by shutting the flapper quicker than the 1.60 GPF toilet or the 1.28 GPF fills less water than 1.60 GPF toilet in the tank? Can anyone explain it?
 
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Jadnashua

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There's more than one way to make this work. Not being flip, but the answer is yes...some rely on less in the bowl, some close the flapper sooner, but it's often a combination. The goal is to get a fast impulse of water to start the siphoning and some do that with a jet, some use pressure assist. The design of that will determine whether it works or not and how well.

In general, a 1.28g flush toilet has a smaller bowl volume than a 1.6g one, but that's not an absolute, either. Toto says they got most of the benefit of the 1.28g from calibrating things closer to avoid excess water going down the drain and shutting the flapper at a more reliable, consistent point. Their 1g unit uses a different bowl.
 

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And their 1.6 and 1.28 toilets use the exact same bowl, now optimized for 1.28.

Toto 1.28 and 1.60 GPF may share the same tank but 1.28 GPF flapper shuts quickly because the flapper has been added weight. See the picture. One may add more weights on the flapper to save more water. Of course, one may take away the weight so that the flapper shuts slowly. Is it the way to change the 1.60 to 1.28 GPF toilet or vice verse?
 
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Jadnashua

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The fill valve's calibration may be slightly more precise as well as the flapper timing. There are some aftermarket, adjustable flapper valves that let you choose. But, on a well-engineered toilet like most Toto designs, trying to redesign them may not really gain much of anything, and in some places, using more water than designed can put you at odds with the controlling authority! Not saying that you'd ever get caught. But, in some places, water is quite dear, and wasting it should be avoided.
 

WJcandee

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That sleeve in the photo is designed to keep the chain from bunching and kinking. It's not there to add weight. Some of the Toto flappers have and have had it, and others that allow the same amount of water through do not. The issue as far as how much water goes through is the buoyancy of the flapper, which is controlled by the amount and size of the side holes in it (as well as other design factors). On the adjustable ones, you adjust buoyancy by covering or uncovering holes and, in the particular tank with a particular-height water column, you thus get the desired amount of water through the valve. The same Toto flapper is used on some 1.6s and some 1.28s. For example, the TSU331s (Korky 2021BP) is used in the 1.6gpf Original Drake, as well as several "Eco"(1.28) toilets, including the Eco Soiree. In the Drake tank, it allows enough through the flush valve to result in a total consumption of 1.6gpf; in the Eco Soiree tank, with its water column and settings, it allows enough through in the flush to produce a total consumption of 1.28gpf (remember, part of the gallons-per-flush measurement is the refill water, so X.XXgpf is measured as the amount of water through the fill valve per cycle, not the amount let out by the flush valve). Other 1.6s and 1.28s have different flappers.

And of course in my post, I was talking about the bowl, not the tank. The Original Drake now uses a bowl optimized for 1.28gpf, regardless of whether you buy the 1.6 or the 1.28 version; the difference is the settings of the guts in the tank, or the guts themselves; the porcelain is the same.
 
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Jadnashua

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Like most anything...design differences can allow multiple ways to achieve the end result. Also, some tend to work better than others. There are always some tradeoffs, either in cost, complexity, or performance. IMHO, Toto does a better job across their available models than most anyone else, but as said, there are always tradeoffs...it's just that their viewpoint tends to align with my preferences.
 
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