generally located behind a panel at the foot of the machine.Some are obvious like little square hatches and some are hidden behind the trim panel at the foot of the machine. Once panel is removed the filter will be seen. Its a circular fitting which generally unscrews in an anticlockwise direction.
Some filters are pretty well disguised by the manufacturers which is a big help to their customers and some machines have no filters at all which allows all manner of debris and detritus directly into the pump.
Check out this site for info: www.2ndwave.co.uk/manual.html
dan, February 2008