"sm_jamieson" wrote in message
oups.com...
After recent trip to US/canada, I have observed that most toilets are
flushed by a type of syphon (or possibly active vaccuum judging by the
force of the suction) which completely empties the toilet bowl before
refilling it. There is a small hole pointing toward the back of the
outlet that refills the bowl. This is nothing like our washdown pans,
or even our vacuum assisted types, where the cistern water causes
partial vaccum in the outlet to assist emptying.
Anyone know more about these US toilets, design and evolution etc.
Of course the bowl syphon is not to be confused with the cistern syphon
(which seems to be dissappearing anyway).
I've also read the archived posts on toilet cubicles with gaps round
the doors, yet highly private urinals with flush, strange I agree.

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.

Brian