surely it could hardly be sold if not fit for purpose as you suggest
If you find a product for mending water butts then doubtless it will do
just that A product advertised for mending plastic water tanks might also
work. All the products I can recollect seeing are for mending pipes or
gutters or pond linings. As these do not usually have 4 or 5 feet deep
water in them they are not subject to as much pressure as you would get in
a water butt. ISTR that you mentioned that the leak was at the bottom of
the butt. The pressure is related to depth of water above the hole. Hence
the popular lower school physics experiment where you take a tall
container and punch holes at the top the middle and the bottom, fill it
with water and observe the relative length of the jets.

Gill M
mmmm well it's only three feet deep, shouldn't get the bends coming up from
that, and the circular shape ought to be quite secure.

Bod at B&Q (not your average mumbling hooded teen joe but a senior citizen
who actually carried around in his pocket a set of photos of the shed he
just built, bit of an enthusiast) reckoned to try flashing tape, the
aluminium (is it?) foil with a layer of tar on one side. I happen to have
some of this so I've given it a try. Perhaps I shall blog about my progress
(!). Failing that he suggested the stuff you waterproof roofs with. And he
gave me Sankey's contact details (they seem a bit shy of the web but phone
is 01159277335 if anyone wants to shout at a minion)