Peter Andrews wrote:

I've connected two butts (at a friends) at the same level by installing a
brass tank connector (15mm) halfway up both butts and connecting both
together with a length of hose. This way the first will fill the second
only when it's a least half full and, as the butts are 40ft apart, there
should always be some water at both ends of the garden as it is impossible
to completely drain both butts from one tap.

I like that.

I am doing something similar with the added refinement of pumps and a
1,000 gallon orange concentrate 'bottle',

Using float switches, 12v pumps will prevent any butt from overflowing
by pumping water from the top part of the butts into the big tank. This
will be around six feet above ground level.

OK, this isn't just for garden use - I shall be using the (soft) water
for washing, flushing the throne, etc, while reducing my water bill. But
there will be a butt in the greenhouse innit.

In my own garden I have four butts connected in series, down a slope,
connected with a hose and the lower ones fitted with ballcocks,

You'll never guess what IRTA...

the overflow
being on the first one by the house.

Always try to site your overflow where it will do most good. Failing
that, least harm.

--
Rusty