As Maggi has noted, a raised bed is a good way to get rid of builders' rubble & other junk. I have made 3 such beds. I've never thought that rubble by itself can 'assist drainage' so, before putting in the soil mix, I washed in coarse sharp sand to fill all the gaps in the rubble.* I do the same thing with troughs & large, free-standing, terracotta, long tom pots but not with smaller plunged pots. I have lots of problems with growing plants but I don't think drainage is one of them.
* I also installed drainage pipes in the beds as Alberto suggests.