Washdown Two-Piece Toilet

A ceramic wash-down two-piece toilet can function with larger trapways than siphonic toilets, but generally require a smaller amount of pre-flush water in the bowl to achieve the 100:1 dilution level required by plumbing codes in most countries.
This small pre-flush volume manifests itself as a small "water spot."  The water spot, or surface area of the pre-flush water in the bowl, plays an important role in maintaining the cleanliness of a ceramic toilet and reducing odors.
A large water spot increases the probability that waste matter will contact water before contacting the ceramic surface of the toilet. This reduces adhesion of waste matter to the ceramic surface making it easier for the toilet to clean itself via the flush cycle. For washdown close-coupled WC compact, with their small water spots therefore frequently require manual cleaning of the bowl after use.
The adhesion of waste material above the water line also leads to a greater level of unpleasant smell during use. But anyway, a larger trapway (usually internal diameter around 85mm) and not easy to result in clogging are already enough reasons for many people to choose wash-down toilet.
In European markets, wash-down two-piece toilets are still more accepted and popular.