Why did those early low-flow toilets clog? Manufacturers begin to think “outside the bowl” to find a solution.
Early 1.6-gpf fixtures - to comply with early-1990s standards - decreased the size of the trapway in order to produce a sufficient siphon to clean and clear the bowl of waste. But in their rush, manufacturers inherently created a chokepoint in the toilets' tight - excuse the expression - colon-like channels.
Today, innovative design and testing capabilities have allowed manufacturers to relieve that traffic jam, all while lowering water consumption even further than mandated.