i had thought of the first method you mention but my fear with that is the overall hight (over 4ft) is greater than the width (front to back) therefore there would be a strong possibility of the whole thing tipping if the center of gravity shifts as it moves over the poles.
i do have a trolly similar to the link posted that i use for water changes but these things have a tendancy to scoot out from under the object if the object is not lowered straight down on to it.
the other option is 2 poles at a right angle to the front, lift one end slide pole in from front to back about 1/4 of way along and same again at the other end, then "walk" the object along the 2 poles. this keeps the correct center of gravity with regards the height being greater than the width and the length is greater than the height so should prevent overtipping sideways.
i am used to back pain, i live with it every day so a wee bit more wont really make any difference, hence the disregard for any injury to myself.
i do realise the best thing is to get help but this is not an easy thing for me to do.
@ TLM
it's ok, you didn't know the full circumstances, i have been driven to desperate measures before and your suggestion did appeal to my sense of humor
![Smile :) :)](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)
for the tank to shift in the way you suggest there would have to be a pretty decent angle and i doubt i will be able to lift/lever it high enough for that.