wrote:

Some loos in the yookay do have an element of siphonic action -
certainly if the water level in the bowl drops right down and then
recovers, then it is not simply washing-down. Totally agree on the
lack of effectiveness of nearly all low-volume units - not met one yet
which worked first-time, which seems to totally negate the point (a low
volume for pees can be achieved with a two-stage flush system). The
powers-that-be have British Standard turds which they claim flush away
nicely with 23ml or whatever but all I can suggest is that they must
bear no resemblance to proper jobs.

We have a double-trap syphonic WC and it's by far the most effective bog
we've ever had. It must have been installed about 25 years ago and
always clears everything at the first attempt. It's also very quiet, so
not too antisocial to flush in the night while others sleep.

When our daughter visists, she often comments about how she wishes she
could get something similar for her house.