the old fox and chicken puzzle

Here's the thing; the builders skip is full.  So is the site.  The skip lorry has come to collect the full one, and deliver an empty one.  But there's nowhere to put the new one, while the old one is lifted on to the lorry.

Hmm - tricky.  Luckily the driver knows the old fox and chicken puzzle.

He lifts the full one onto the lorry and places it on top of the empty one.  Then he lifts the empty one (with the full one inside it) and places it on the ground in the space reserved for it.  

Then he lifts the full one again, leaving the empty one behind and puts it on to the lorry.  Simples.