We use a toilet fill valve. Simple and cheap and effective. Anchored by
cutting a round hole in a tupperware container with rocks in it. We use
the kind with the float right on the shaft of the valve. It just goes
up and down that way. A ballcock extending out would be very vulnerable
to bumping and tipping.

We have a pic on our website. Website below.

Jim

wrote:
I am going to try the toilet valve to create a auto top off system for
my barrel.

Do I just go to hardware store and buy the whole toilet valve assembly
with the floating ball, etc?

How do I make it stand on my barrel?

Is there smaller sized valve available so that it won't take up so much
space?