"Simon Elliott" wrote in message
...
Andy Hall writes

[snip]
Thanks for the suggestions and links

Basically you need to reduce the flow rate into the cistern to a level
that the overflow can manage.

Makes sense. I was looking at the problem from the angle of "how do I
get the overflow to cope with the flow rate", but it's probably easier
to solve "how do I reduce the flow rate so that the overflow can cope
with it".

Andy obviously has the real answer but simply a wider diameter overflow
would allow more water to flow out faster.