Larry Mayo asks about a solvent for silicone adhesive. Once it is
cured, I don't know of anything pleasant that will dissolve it. You
can call the company (GE - DOW - etc.) and get some information.
But I hope you are asking about making it less viscous, i.e., more
runny. The answer is to add some naphtha. You can go out and buy some
lighter fluid for $3 an ounce or you can just buy a quart for $2.50 at
the hardware store.
You may also know that there are a lot of different types and colors
of silicone sealant. I have found the black stuff particularly handy.
In fact, you can buy a tube that is already 'thin'.
There are also 3 types of sealant. The familiar one has a vinegar
smell and cures with acetic acid. There is another that is alcohol
based instead. It is used to 'pot' electrical parts because the acid
would cause a problem.
I bought some of the alcohol based silicone to use for the same reason
and I expected to be able to thin it with alcohol. Big surprise.
Water won't work either. Back to the naphtha an both cases.
Another thing you should know: if you mix the naphtha at 50% by volume,
it will harden pretty much as normal. However, after a few days a
1"x1"x1" cube will become a 3/4" cube.