20x20 inches, 25 feet tall.
Originally 8" liner with red brick.
Lined with 6" stainless set in place with a mortar of vermiculite.

And then- once I know how much it weighs- if I was to brace it with a
support set at a 25degree angle, how strong a support do I need? Steel
or wood?

Really long story- shortened; It has sat on a 8 foot high pillar of
clay about 3x3 in my basement for 20 years. I want to remove the
clay one side at a time and pour a 4x4 footing and a 2foot column. The
'temporary' bracing that was put in when the job was done will have to
be removed to dig the footing.

To dig the first 1/2 I won't need to disturb 2 sides of the base- and
I know it is tied to a slab that will be undisturbed. The support
will be an extra safety- hopefully not needed.

thanks-
Jim