Thank you for your post. Movement of the tank is underway as I type.
So far, we have been able to jack both ends up and put 2x4 pieces under
them. We have screwed casters (strong enough for 1000 lbs) onto some
2x6 (double rows of casters). Tomorrow we will attempt to jack up the
tank and slide the caster planks in place and try to actually move the
tank. In looking at the wood that we jacked the legs onto, there was
no impression left, which seems to me that the weight is either
distributed rather evenly, or the tank is not as heavy as we thought.

Thanks again for your post. This is certainly a slow process. Not
sure in the long run if it would have been better to pay a
"professional" to do it, but that would have cost us $700 to have
someone move it!!! So, for less than $50 in parts and tools, we're
trying it! Could be a disaster, but I'll let you know if it works.