"Dick Adams" wrote
Percival P. Cassidy wrote:

I have lived both in Australia and in Taiwan. In both
countries, bathroom floors had drains to avoid serious
flooding in the case of overflows. ..

Why have I never encountered such in US bathrooms?

Also in the States, most county/city plumbing codes does
not allow waste water to be dumped on to the ground.

Dick, you nailed it. USA safety codes do not allow 'grey water' dumping.
It has to go to a septic or sewer. So his actual design (flowing to the
ground outside) isnt legal here.

We do sometimes have floor drains, most often in public restrooms or gyms,
but they lead to the sewer lines.

Laws in OZ are not the same. They allow for grey water diferences. Such as
recycling the shower water to the toilet for flushing. It's based on their
lower fresh water amounts than we generally have so adaptions have been
made.

Now in Japan, you will have 2 rooms vice 1 like in the USA. One has a
toilet and may have a sink (often over the back of the toilet tank and
frequently with those no hot water tap). This drains right into the water
holding tank for flushing the toilet. This is called 'the toilet room'.

The other room is the bathing room or 'bathroom', often has laundry setups
in there separated by a glass door from the actual bathing portion. Will
have a sink, a tub (deeper than USA ones usually) and a hand held showering
device with a long cable.

You wash outside the tub enclosure first then hang the handle up and step in
the tub (after washing off and rinsing down into the floor drain). The
handheld showerhead may have a wall fixture with several heights (some of
which are child shower and some adult) but it will not be over the tub most
likely. Reason is, you wash before you get in there, not while in there'.
The fancy traps that catch hair etc, are in the floor drain and not in the
tub drain.