"sm_jamieson" wrote in message
ups.com...
How odd, I've also just returned from a US trip and was pondering the
exact
some thing while I was there. I asked a friend out there (also a DIYer)
and
he said the flush worked in the same way (at least in the pan, the
cistern
part tends to use a "flap valve", which is now available in the UK). As
we
had along wait at the airport, I had some time to think on the problem.

The "throat" of the bowl seemed much smaller and there is a large "pool"
of
water in bowl. (Good idea to keep the bowl clean). I wonder if these
factors
combined give a "quick flush" that looks like a vacuum. The U seemed
quite
tight, so maybe the action is like this:

Bowl full, level will form at the U top lip. When you flush, a water is
added slowly (compared to the UK) until there is enough to start the
flush,
which progresses quickly as there is a lot of "head" in the bowl. So
fast,
the bowl empties before enough fresh water gets in to maintain syphon
level.
Syphon stops and bowl refills.

Yep, I think the crucial thing is that it is actually a syphon, so it
continues with little head of water to maintain it. With our wash-down
pans, water added just pushes out the "stuff" like a normal u-bend,
which is why the new 6 litre things are so feeble.

We had a siphon cistern and washdown pan. The yanks had the opposite.