"Simon Avery" wrote in message
...
"Des" wrote:


I had this same question. The ceramic cistern has no hole for a
conventional overflow. The instructions for the flush assembly DO
mention an internal overflow but it's by no means apparent that what
you're given is such a beast.

However... When I hold down the ballcock on mine to simulate an
overflow, water DOES drain down to the pan (as per the new regs that
allow an internal overflow). I have absolutely no idea how it does
this - there's no physical difference to the assembly compared to a
normal one, but it "just works", so I stopped worrying about it.
....
It could be you don't have the internal overflow gubbins inside

There's no extra gubbins: water simply flows over the top of the
inverted-U-shaped part of the syphon assembly and down into the pan. The
only difference between that and a bog[sorry] standard arrangement is the
relative levels of the top of the syphon and the external overflow on
conventional cisterns which allow water to reach the top of the syphon - on
a normal cistern water would reach the overflow outlet first.

It
doesn't drain enough to cope with a full blown entry failure, but then
- a 21.5mm conventional overflow often wouldn't either.

It should be able to cope with practically full-bore mains flow into the
cistern, but for some reason cistern makers do like to put stupid cutouts
into the back of the cistern for no apparent reason which compromise the
design.

As for the question of which type of overflow is more easily visible, I
think a drip is more visible from an external pipe, but I've seen external
pipes in inconspicuous (even invisible) places where a minor river can (and
in some cases I've seen, does) discharge without anyone noticing, which they
would with an overflow down the pan.