When moving any tank, I'd take everything out, including gravel. 70 ltr may not sound big, but if you're carrying it downstairs all you'll need to do is lean slightly the wrong way and you'll be needing a new tank - and possibly a visit to hospital. However small you may think the risk is, it's just not worth it, IMO.
I'd have to agree. I've moved tanks before, that were part filled (albeit only a few feet) but it is never recommended. You may be fine, but there is always the posibility that you put pressure on a weak spot of the tank and then you have alot of glass, water and livestock to clean up. For the extra bit of effort it will take to remove eveything, I'd do it. If you can get a new dustbin, these make excellent containers if you wish to keep your water etc.