Assuming your tap has a threaded spout:
One of these on the tap and one on the pressure washer:
One of these on the tap end of the hose: http://www.amazon.co.uk/Hozelock-2050-Hose-End-Connector/dp/B001OXFHVY
One of these on the other end of the hose:
And a hose, of course.
Pop down to a garden centre!!