nicktheplumber
Because of the 1.6 gallon “Federal Flush” regulation, your toilet must be engineered to work extremely efficiently. There is hardly any margin for error. In the good old days, 3.5+ gallon flushers hardly ever presented problems, even the inherently inefficient designs, such as the “wash down.”
I’m really not sure how the authorities settled on 1.6 gallons as the “optimal” flush volume, but we bonehead plumbers are stuck with it. We depend on the toilet-maker’s engineers to provide units that work under the legal constraints. Some of them do and some of them don’t. One brand that seems to always work well is the Toto, especially their G-max system. You can also go for various pressure-assisted toilets. These do flush better, but I don’t like them because they are more complex and therefore more prone to failure, eventually. Also, they are all damned noisy…
Retired Plumbing made a good observation. Many cheaper 1.6 gal flushers fail to flush well because the ball (flapper) valve closes a bit too early in the flush cycle. This can be fixed by having the homeowner take the extra effort to hold the flush lever down for a few extra seconds, to make sure the tank discharges completely during the flush.
