wrote:

Actually it's not really a food item, but I have a plastic
(Rubbermaid) livestock tank that has a hole in it from the
tank heater melting thru it. I'm thinking about using a piece
of tin, putting 100% pure silicone on the tin, and bolting it
thru the plastic. But is silicone safe for this sort of use?

It certainly is.

There is food-grade silicone, I've seen a few tubes in local hardware
stores:

http://www-img.toolstation.com/image...bbig/99477.jpg

And also remember that breast implants are made with a tough outer
membrane made from silicone.

Pace maker leads have a jacket material that is made from silicone.