Jadnashua
Retired Defense Industry Engineer xxx
To flush a toilet with a small amount of water, you need a spurt of water fast. There are basically three ways to do that: larger flapper, pressure assist, and larger pipe (generally only used in commercial units because the average home doesn't have the water pipe size required). The goal is to get the water moving fast enough to create a siphon so it can carry the waste efficiently out of the bowl and then shut the water use off so that it stays within the mandated max. Older toilets may have used as much as 8 gallons or more and took their time about it. Getting it from that outlet point to the rest of the drain is important, too, since the shape of that trapway will affect the velocity and whether things need to slow down as they exit. This is where smoother curves are better - for less restrictions to keep the speed up, and for minimizing clogs in case you're trying to flush brick hard logs. The size of the trapway is important, too, but since most people's waste is at least moderately pliable, you can get by with a less optimized design most of the time. To get a super large trapway, you need just that much more initial water velocity (assuming the same amount of water is used) to get it to siphon and clear the bowl. One reason the Caroma may splash a little (flush after you get up!). Getting all of the pieces right and making a reliably good product points to the winners in this race. Some get it right on a regular basis, some don't. Since everyone's different, what works for one may not work for another. There is no one toilet that will work for everyone because their priorities are different: style, color, size, performance, cost. The experience here, and mine personally, is that for me anyway, Toto both performs well, and fit my needs. That may not be true for you. But from a reliable viewpoint, and parts availability and ease of eventual repair, unless you get one of their exotics that can cost into the thousands of dollars, they are easily serviced with readily available and inexpensive parts. This isn't necessarily true for others (it varies from easy like the Toto, to a major pain on some others). Any time someone comes up with a new design on a flapper or fill valve and it's proprietary, or not common, you're asking for at least an annoyance, if not plain trouble and maybe excessive costs.