In article , says...
In a polythene bag. Drag over floor until bag is covered with screws,
then turn bag inside-out and remove magnet.

Or if you want to do it industrially...

http://www.machinemart.co.uk/shop/pr...agnetic-floor-
sweeper/path/parts-washers-blast-cabinets

You can get hand-held ones, too.
--
Skipweasel.
Never knowingly understood.