Six of us, but with a lack of planning, a high stand and a confined space it nearly ended in tears. We didn't think about who was where when we lifted the tank and when the ones on the back moved around so we could lift it onto the stand we ended up with four strong guys on the front and two shorter and not-so-strong guys on the corners. The front went up but the back didn't, there was a lot of grunting and shouting, one guy was even underneath it lifting with his shoulder, and eventually we got it onto the stand.
I don't mind helping if I'm free on the day, I'll hopefully need some big-tank-lifting credits in the not too distant future... 8)