How to empty brown garden bin?

Moved into a property and it's completely full up in renting of a social landlord. I suspect it belongs to other people the contents but they're denying it's theirs so I've arranged for it to be collected as it's not needed. However, it needs to be empty. How do I empty it? I don't have any garden tools such as a spade, I could possibly lay it on the ground and turn it upside down. I can't think of another way but this would create a huge mess. What would you do? I wasn't sure whether to just put black bin liners on the floor, empty it and then scoop it all up into black bin bags with my dust pan and brush pan. I really can't think what to do with it.