Okay, moving on from grey water to black water, or rather getting
"water" into the cistern.

Does anyone have any practical experience of how much head of water you
need to refill a toilet cistern from a water tank. No Pump.

Looking for head and feed pipe size.

Are there special low pressure float valves?

The standard inlet size to the toilet cistern float valve is about 1/2"
(?metric), however, I figure that if I run the standard 1"/25mm tank
interconnect feed into it, then I will not have to worry about length of
feed and the real question then is what head of water I need.

Since Sydney seems to have gone back to wettish weather and the tanks
are mostly full, I figure it is now time to get serious about using
rainwater (and grey water?) for toilet flushing.

my plan is to extend the rainwater storage by adding a thin tank on the
side path that can collect (some of) the surplus rainwater from the
overflows. I would also have bottom feed if I can get a suitable
non-return valve.

Given location, it would be feasible to dump the washing machine
greywater into it.

Head would be maintained in dry weather by float value from mains.

I am definitely not moving to electric pump assisted[1]. Maurice the
Lemming has started sending out reassurance letters to pensioners about
the forthcoming changes to NSW electricity, which means bills are going
to sky rocket.


[1] Anyone charging a tank with PV powered pump?