"Terryc" wrote in message
FarmI wrote:

Yes. Looking for ideas on refill times and how far above the top of the
toilet cistern I need to place the mains top up float valve.

??? You asked about filling the cistern from your tank.

Correct, but when the tank level gets too low, I'll need to add water to
the tank to keep the toilet flushing until the tank it is topped up with
the next rain.

Having the mains top up float as low as possible means that I use as
little as possible mains water.

Do not confuse it with my greywater discussions.

I wasn't. I was responding directly and only to your water tank question.

So I am looking at gravity feed version. It just means there is less of
the tank available and the mains top off float valve is installed higher.

In practice, unless we had a run of dry weather, the tap for the mains top
off would only be turned on when needed.

What I am trying to avoid is finding that 1' above cistern head allows for
one flush a day by the time it reflls.

???? The time to refill will depend on the size off the pipe. As I wrote
earlier, if you use a quarter inch drip line it would take a long time. If
you use a half or one inch pipe it will take minutes.

The bigger concern for only 1' of water above the cistern would be the size
of your water tank. If you have one of those minute tanks that seem to be
popular in the city then only 1' of water will mean tuening on the mains
again pdq. If you have a 2,000 gall tank then 1' of water will flush for a
long time.

If someone comes back and says that you really need 3', then it is a no
goer as not worth the effort with the existing tanks, unless I somehow hit
upon a very cheap supply of tall, thin water tanks that will fit up the
side path. (which has lost is effectiveness as a second side path when the
new "better insulated" water heater had to go outside).

As I explained earlier, you only need the level of the water in your tank to
be above the inlet to your cistern. That is why I wrote about how farmers
use the plastic pipe to move water from the irrigation channel which is only
a few inches higher into their paddocks.

Water will always flow to a lower level and try to equalise it's level.
Just think of this as a very simple but effective devise used to build - a
hose with water and 2 clear plastic ends added to the tube - the water in
each clear plastic end gives a level that is true and accurate.