"Richard J Kinch" wrote in message
. ..
Anyway, my thought was to fill some already pressure resistant
device
such as a pressure cooker or autoclave chamber (hello ebay!) with
water
and then use shop air to increase the pressure.

Corny kegs, formerly used by soda fountains, but now mostly used as
surplus
items in the home brewing hobby, are cheap ($10 surplus), have a
nice big
opening, have a 100 psi working pressure, last forever (all
stainless), and
are easily resold. A homebrew hobby supplier will also have the
fittings
to connect your shop air.

I've got one of those in my garage, but I don't think something 6X6
will fit through the opening....